diff --git a/History.md b/History.md
index 94e8e7bca50..ffc73974aab 100644
--- a/History.md
+++ b/History.md
@@ -1,3 +1,20 @@
+4.6.5 / 2016-10-23
+==================
+ * docs: fix grammar issues #4642 #4640 #4639 [silvermanj7](https://github.com/silvermanj7)
+ * fix(populate): filter out nonexistant values for dynref #4637
+ * fix(query): handle $type as a schematype operator #4632
+ * fix(schema): better handling for uppercase: false and lowercase: false #4622
+ * fix(query): don't run transforms on updateForExec() #4621
+ * fix(query): handle id = 0 in findById #4610
+ * fix(query): handle buffers in mergeClone #4609
+ * fix(document): handle undefined with conditional validator for validateSync #4607
+ * fix: upgrade to mongodb driver 2.2.11 #4581
+ * docs(schematypes): clarify schema.path() #4518
+ * fix(query): ensure path is defined before checking in timestamps #4514
+ * fix(model): set version key in upsert #4505
+ * fix(document): never depopulate top-level doc #3057
+ * refactor: ensure sync for setting non-capped collections #2690
+
 4.6.4 / 2016-10-16
 ==================
  * fix(query): cast $not correctly #4616 #4592 [prssn](https://github.com/prssn)
diff --git a/docs/guide.jade b/docs/guide.jade
index 00edbc2e54d..8b18ca90cac 100644
--- a/docs/guide.jade
+++ b/docs/guide.jade
@@ -127,7 +127,7 @@ block content
 
   h3#query-helpers Query Helpers
   :markdown
-    You can also add query helper functions, which are like instance methods,
+    You can also add query helper functions, which are like instance methods
     but for mongoose queries. Query helper methods let you extend mongoose's
     [chainable query builder API](./queries.html).
     
diff --git a/docs/populate.jade b/docs/populate.jade
index fc148f44cf3..5bc7a0387d7 100644
--- a/docs/populate.jade
+++ b/docs/populate.jade
@@ -344,6 +344,19 @@ block content
     Band.find({}).populate('members').exec(function(error, bands) {
       /* `bands.members` is now an array of instances of `Person` */
     });
+  
+  :markdown
+    Keep in mind that virtuals are _not_ included in `toJSON()` output by
+    default. If you want populate virtuals to show up when using functions
+    that rely on `JSON.stringify()`, like Express'
+    [`res.json()` function](http://expressjs.com/en/4x/api.html#res.json),
+    set the `virtuals: true` option on your schema's `toJSON` options.
+  
+  :js
+    // Set `virtuals: true` so `res.json()` works
+    var BandSchema = new Schema({
+      name: String
+    }, { toJSON: { virtuals: true } });
 
   h3#next Next Up
   :markdown
diff --git a/docs/schematypes.jade b/docs/schematypes.jade
index c0a74ee8891..06bbe96393c 100644
--- a/docs/schematypes.jade
+++ b/docs/schematypes.jade
@@ -244,6 +244,26 @@ block content
     | To create your own custom schema take a look at 
     a(href="/docs/customschematypes.html") Creating a Basic Custom Schema Type
     |.
+    
+  h3#path The `schema.path()` Function
+  :markdown
+    The `schema.path()` function returns the instantiated schema type for a
+    given path.
+  :js
+    var sampleSchema = new Schema({ name: { type: String, required: true } });
+    console.log(sampleSchema.path('name'));
+    // Output looks like:
+    /**
+     * SchemaString {
+     *   enumValues: [],
+     *   regExp: null,
+     *   path: 'name',
+     *   instance: 'String',
+     *   validators: ...
+     */
+  :markdown
+    You can use this function to inspect the schema type for a given path,
+    including what validators it has and what the type is.
 
   h3#next Next Up
   :markdown
diff --git a/docs/subdocs.jade b/docs/subdocs.jade
index e32b7927dc0..90a4306eca7 100644
--- a/docs/subdocs.jade
+++ b/docs/subdocs.jade
@@ -4,7 +4,7 @@ block content
   h2 Sub Docs
   :markdown
     [Sub-documents](./api.html#types-embedded-js) are docs with schemas of
-    their own which are elements of a parents document array:
+    their own which are elements of a parent document array:
   :js
     var childSchema = new Schema({ name: 'string' });
 
@@ -24,7 +24,7 @@ block content
     parent.save(callback);
 
   :markdown
-    If an error occurs in a sub-documents' middleware, it is bubbled up to the `save()` callback of the parent, so error handling is a snap!
+    If an error occurs in a sub-document's middleware, it is bubbled up to the `save()` callback of the parent, so error handling is a snap!
 
   :js
     childSchema.pre('save', function (next) {
@@ -104,8 +104,8 @@ block content
     });
   :markdown
     A single embedded sub-document behaves similarly to an embedded array.
-    It only gets saved when the parent document gets saved, and its pre/post
-    document middleware get executed.
+    It only gets saved when the parent document gets saved and its pre/post
+    document middleware gets executed.
   :js
     childSchema.pre('save', function(next) {
       console.log(this.name); // prints 'Leia'
diff --git a/lib/cast.js b/lib/cast.js
index 3f687d0d7f8..6a071969dad 100644
--- a/lib/cast.js
+++ b/lib/cast.js
@@ -196,13 +196,6 @@ module.exports = function cast(schema, obj) {
               continue;
             }
 
-            if ($cond === '$type') {
-              if (typeof nested !== 'number' && typeof nested !== 'string') {
-                throw new Error('$type parameter must be number or string');
-              }
-              continue;
-            }
-
             if ($cond === '$not') {
               if (nested && schematype && !schematype.caster) {
                 _keys = Object.keys(nested);
diff --git a/lib/document.js b/lib/document.js
index 8d460f3ee44..1c20ae29445 100644
--- a/lib/document.js
+++ b/lib/document.js
@@ -2023,17 +2023,13 @@ Document.prototype.$toObject = function(options, json) {
     retainKeyOrder: this.schema.options.retainKeyOrder
   };
 
-  if (options && options.depopulate && !options._skipDepopulateTopLevel && this.$__.wasPopulated) {
+  // _isNested will only be true if this is not the top level document, we
+  // should never depopulate
+  if (options && options.depopulate && options._isNested && this.$__.wasPopulated) {
     // populated paths that we set to a document
     return clone(this._id, options);
   }
 
-  // If we're calling toObject on a populated doc, we may want to skip
-  // depopulated on the top level
-  if (options && options._skipDepopulateTopLevel) {
-    options._skipDepopulateTopLevel = false;
-  }
-
   // When internally saving this document we always pass options,
   // bypassing the custom schema options.
   if (!(options && utils.getFunctionName(options.constructor) === 'Object') ||
@@ -2065,6 +2061,8 @@ Document.prototype.$toObject = function(options, json) {
   // to save it from being overwritten by sub-transform functions
   var originalTransform = options.transform;
 
+  options._isNested = true;
+
   var ret = clone(this._doc, options) || {};
 
   if (options.getters) {
diff --git a/lib/drivers/node-mongodb-native/collection.js b/lib/drivers/node-mongodb-native/collection.js
index 7e88140b2c2..9bb1bef4b9e 100644
--- a/lib/drivers/node-mongodb-native/collection.js
+++ b/lib/drivers/node-mongodb-native/collection.js
@@ -40,7 +40,8 @@ NativeCollection.prototype.onOpen = function() {
 
   if (!_this.opts.capped.size) {
     // non-capped
-    return _this.conn.db.collection(_this.name, callback);
+    callback(null, _this.conn.db.collection(_this.name));
+    return _this.collection;
   }
 
   // capped
diff --git a/lib/model.js b/lib/model.js
index 7583a852f95..c1a198baafc 100644
--- a/lib/model.js
+++ b/lib/model.js
@@ -407,7 +407,7 @@ function handleAtomics(self, where, delta, data, value) {
     // $set
 
     if (isMongooseObject(value)) {
-      value = value.toObject({depopulate: 1});
+      value = value.toObject({depopulate: 1, _isNested: true});
     } else if (value.valueOf) {
       value = value.valueOf();
     }
@@ -417,7 +417,7 @@ function handleAtomics(self, where, delta, data, value) {
 
   function iter(mem) {
     return isMongooseObject(mem)
-        ? mem.toObject({depopulate: 1})
+        ? mem.toObject({depopulate: 1, _isNested: true})
         : mem;
   }
 
@@ -426,7 +426,7 @@ function handleAtomics(self, where, delta, data, value) {
     val = atomics[op];
 
     if (isMongooseObject(val)) {
-      val = val.toObject({depopulate: true, transform: false});
+      val = val.toObject({depopulate: true, transform: false, _isNested: true});
     } else if (Array.isArray(val)) {
       val = val.map(iter);
     } else if (val.valueOf) {
@@ -506,7 +506,7 @@ Model.prototype.$__delta = function() {
       value = value.toObject();
       operand(this, where, delta, data, value);
     } else {
-      value = utils.clone(value, {depopulate: 1});
+      value = utils.clone(value, {depopulate: 1, _isNested: true});
       operand(this, where, delta, data, value);
     }
   }
@@ -1556,7 +1556,7 @@ Model.findOneAndUpdate = function(conditions, update, options, callback) {
     fields = options.fields;
   }
 
-  update = utils.clone(update, {depopulate: 1});
+  update = utils.clone(update, {depopulate: 1, _isNested: true});
   if (this.schema.options.versionKey && options && options.upsert) {
     if (!update.$setOnInsert) {
       update.$setOnInsert = {};
@@ -2081,6 +2081,13 @@ Model.update = function update(conditions, doc, options, callback) {
   }
   options = typeof options === 'function' ? options : utils.clone(options);
 
+  if (this.schema.options.versionKey && options && options.upsert) {
+    if (!doc.$setOnInsert) {
+      doc.$setOnInsert = {};
+    }
+    doc.$setOnInsert[this.schema.options.versionKey] = 0;
+  }
+
   return mq.update(conditions, doc, options, callback);
 };
 
@@ -2927,6 +2934,11 @@ function getModelsMapForPopulate(model, docs, options) {
 
     if (refPath) {
       modelNames = utils.getValue(refPath, doc);
+      if (Array.isArray(modelNames)) {
+        modelNames = modelNames.filter(function(v) {
+          return v != null;
+        });
+      }
     } else {
       if (!modelNameFromQuery) {
         var modelForCurrentDoc = model;
diff --git a/lib/query.js b/lib/query.js
index a02873371bf..136934d5723 100644
--- a/lib/query.js
+++ b/lib/query.js
@@ -946,7 +946,11 @@ Query.prototype.getUpdate = function() {
  */
 
 Query.prototype._updateForExec = function() {
-  var update = utils.clone(this._update, { retainKeyOrder: true });
+  var update = utils.clone(this._update, {
+    retainKeyOrder: true,
+    transform: false,
+    depopulate: true
+  });
   var ops = Object.keys(update);
   var i = ops.length;
   var ret = {};
diff --git a/lib/schema.js b/lib/schema.js
index adb76dc5425..45cd986d8ea 100644
--- a/lib/schema.js
+++ b/lib/schema.js
@@ -878,10 +878,12 @@ function applyTimestampsToChildren(query) {
   if (hasDollarKey) {
     if (update.$push) {
       for (key in update.$push) {
+        var $path = schema.path(key);
         if (update.$push[key] &&
-            schema.path(key).$isMongooseDocumentArray &&
-            schema.path(key).schema.options.timestamps) {
-          timestamps = schema.path(key).schema.options.timestamps;
+            $path &&
+            $path.$isMongooseDocumentArray &&
+            $path.schema.options.timestamps) {
+          timestamps = $path.schema.options.timestamps;
           createdAt = timestamps.createdAt || 'createdAt';
           updatedAt = timestamps.updatedAt || 'updatedAt';
           update.$push[key][updatedAt] = now;
diff --git a/lib/schema/number.js b/lib/schema/number.js
index 3fec612dc43..a91f6dda6df 100644
--- a/lib/schema/number.js
+++ b/lib/schema/number.js
@@ -203,9 +203,9 @@ SchemaNumber.prototype.cast = function(value, doc, init) {
     return ret;
   }
 
-  var val = value && value._id
-      ? value._id // documents
-      : value;
+  var val = value && typeof value._id !== 'undefined' ?
+    value._id : // documents
+    value;
 
   if (!isNaN(val)) {
     if (val === null) {
diff --git a/lib/schema/string.js b/lib/schema/string.js
index 02ff495f934..cf49af6dbfc 100644
--- a/lib/schema/string.js
+++ b/lib/schema/string.js
@@ -129,7 +129,10 @@ SchemaString.prototype.enum = function() {
  * @return {SchemaType} this
  */
 
-SchemaString.prototype.lowercase = function() {
+SchemaString.prototype.lowercase = function(shouldApply) {
+  if (arguments.length > 0 && !shouldApply) {
+    return this;
+  }
   return this.set(function(v, self) {
     if (typeof v !== 'string') {
       v = self.cast(v);
@@ -155,7 +158,10 @@ SchemaString.prototype.lowercase = function() {
  * @return {SchemaType} this
  */
 
-SchemaString.prototype.uppercase = function() {
+SchemaString.prototype.uppercase = function(shouldApply) {
+  if (arguments.length > 0 && !shouldApply) {
+    return this;
+  }
   return this.set(function(v, self) {
     if (typeof v !== 'string') {
       v = self.cast(v);
diff --git a/lib/schematype.js b/lib/schematype.js
index 8c796d9bb18..3ca3423618b 100644
--- a/lib/schematype.js
+++ b/lib/schematype.js
@@ -776,12 +776,16 @@ SchemaType.prototype.doValidateSync = function(value, scope) {
     }
   };
 
-  var _this = this;
-  if (value === undefined && !_this.isRequired) {
-    return null;
+  var validators = this.validators;
+  if (value === void 0) {
+    if (this.validators.length > 0 && this.validators[0].type === 'required') {
+      validators = [this.validators[0]];
+    } else {
+      return null;
+    }
   }
 
-  this.validators.forEach(function(v) {
+  validators.forEach(function(v) {
     if (err) {
       return;
     }
@@ -874,7 +878,14 @@ SchemaType.prototype.$conditionalHandlers = {
   $eq: handleSingle,
   $in: handleArray,
   $ne: handleSingle,
-  $nin: handleArray
+  $nin: handleArray,
+  $type: function(val) {
+    if (typeof val !== 'number' && typeof val !== 'string') {
+      throw new Error('$type parameter must be number or string');
+    }
+
+    return val;
+  }
 };
 
 /**
diff --git a/lib/types/array.js b/lib/types/array.js
index e63c02367e8..715b6b65afb 100644
--- a/lib/types/array.js
+++ b/lib/types/array.js
@@ -232,7 +232,7 @@ MongooseArray.mixin = {
     var i = keys.length;
 
     if (i === 0) {
-      ret[0] = ['$set', this.toObject({depopulate: 1, transform: false})];
+      ret[0] = ['$set', this.toObject({depopulate: 1, transform: false, _isNested: true})];
       return ret;
     }
 
@@ -244,9 +244,9 @@ MongooseArray.mixin = {
       // need to convert their elements as if they were MongooseArrays
       // to handle populated arrays versus DocumentArrays properly.
       if (isMongooseObject(val)) {
-        val = val.toObject({depopulate: 1, transform: false});
+        val = val.toObject({depopulate: 1, transform: false, _isNested: true});
       } else if (Array.isArray(val)) {
-        val = this.toObject.call(val, {depopulate: 1, transform: false});
+        val = this.toObject.call(val, {depopulate: 1, transform: false, _isNested: true});
       } else if (val.valueOf) {
         val = val.valueOf();
       }
@@ -713,6 +713,7 @@ MongooseArray.mixin = {
 
   toObject: function(options) {
     if (options && options.depopulate) {
+      options._isNested = true;
       return this.map(function(doc) {
         return doc instanceof Document
             ? doc.toObject(options)
diff --git a/lib/types/subdocument.js b/lib/types/subdocument.js
index 606cfa76ce6..911fdf44093 100644
--- a/lib/types/subdocument.js
+++ b/lib/types/subdocument.js
@@ -19,7 +19,7 @@ Subdocument.prototype = Object.create(Document.prototype);
 
 Subdocument.prototype.toBSON = function() {
   return this.toObject({ transform: false });
-},
+};
 
 /**
  * Used as a stub for [hooks.js](https://github.com/bnoguchi/hooks-js/tree/31ec571cef0332e21121ee7157e0cf9728572cc3)
diff --git a/lib/utils.js b/lib/utils.js
index a5aa720060a..391325f0641 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -840,6 +840,9 @@ exports.mergeClone = function(to, fromObj) {
         if (isMongooseObject(fromObj[key]) && !fromObj[key].isMongooseBuffer) {
           obj = obj.toObject({ transform: false });
         }
+        if (fromObj[key].isMongooseBuffer) {
+          obj = new Buffer(obj);
+        }
         exports.mergeClone(to[key], obj);
       } else {
         // make sure to retain key order here because of a bug handling the
diff --git a/package.json b/package.json
index 7429a4b6e1a..8ccd487c5f9 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "mongoose",
   "description": "Mongoose MongoDB ODM",
-  "version": "4.6.4",
+  "version": "4.6.5",
   "author": "Guillermo Rauch <guillermo@learnboost.com>",
   "keywords": [
     "mongodb",
@@ -23,7 +23,7 @@
     "bson": "~0.5.4",
     "hooks-fixed": "1.2.0",
     "kareem": "1.1.3",
-    "mongodb": "2.2.10",
+    "mongodb": "2.2.11",
     "mpath": "0.2.1",
     "mpromise": "0.5.5",
     "mquery": "2.0.0",
@@ -46,7 +46,7 @@
     "markdown": "0.3.1",
     "marked": "0.3.6",
     "mocha": "3.0.2",
-    "mongoose-long": "0.1.0",
+    "mongoose-long": "0.1.1",
     "node-static": "0.7.7",
     "power-assert": "1.2.0",
     "q": "1.4.1",
diff --git a/test/document.test.js b/test/document.test.js
index 89475867bb7..b14d6667f4d 100644
--- a/test/document.test.js
+++ b/test/document.test.js
@@ -3254,6 +3254,30 @@ describe('document', function() {
         catch(done);
     });
 
+    it('validateSync with undefined and conditional required (gh-4607)', function(done) {
+      var schema = new mongoose.Schema({
+        type: mongoose.SchemaTypes.Number,
+        conditional: {
+          type: mongoose.SchemaTypes.String,
+          required: function() {
+            return this.type === 1;
+          },
+          maxlength: 128
+        }
+      });
+
+      var Model = db.model('gh4607', schema);
+
+      assert.doesNotThrow(function() {
+        new Model({
+          type: 2,
+          conditional: void 0
+        }).validateSync();
+      });
+
+      done();
+    });
+
     it('setting full path under single nested schema works (gh-4578) (gh-4528)', function(done) {
       var ChildSchema = new mongoose.Schema({
         age: Number
@@ -3280,6 +3304,21 @@ describe('document', function() {
       });
     });
 
+    it('toObject() does not depopulate top level (gh-3057)', function(done) {
+      var Cat = db.model('gh3057', { name: String });
+      var Human = db.model('gh3057_0', {
+        name: String,
+        petCat: { type: mongoose.Schema.Types.ObjectId, ref: 'gh3057' }
+      });
+
+      var kitty = new Cat({ name: 'Zildjian' });
+      var person = new Human({ name: 'Val', petCat: kitty });
+
+      assert.equal(kitty.toObject({ depopulate: true }).name, 'Zildjian');
+      assert.ok(!person.toObject({ depopulate: true }).petCat.name);
+      done();
+    });
+
     it('modify multiple subdoc paths (gh-4405)', function(done) {
       var ChildObjectSchema = new Schema({
         childProperty1: String,
diff --git a/test/model.findOneAndUpdate.test.js b/test/model.findOneAndUpdate.test.js
index bddb45eb580..5c87913b591 100644
--- a/test/model.findOneAndUpdate.test.js
+++ b/test/model.findOneAndUpdate.test.js
@@ -964,7 +964,7 @@ describe('model: findByIdAndUpdate:', function() {
     }
   });
 
-  it('adds __v on upsert (gh-2122)', function(done) {
+  it('adds __v on upsert (gh-2122) (gh-4505)', function(done) {
     var db = start();
 
     var accountSchema = new Schema({
@@ -974,14 +974,21 @@ describe('model: findByIdAndUpdate:', function() {
     var Account = db.model('2122', accountSchema);
 
     Account.findOneAndUpdate(
-        {name: 'account'},
-        {},
-        {upsert: true, new: true},
-        function(error, doc) {
+      {name: 'account'},
+      {name: 'test'},
+      {upsert: true, new: true},
+      function(error, doc) {
+        assert.ifError(error);
+        assert.equal(doc.__v, 0);
+        Account.update({ name: 'test' }, {}, { upsert: true }, function(error) {
           assert.ifError(error);
-          assert.equal(doc.__v, 0);
-          db.close(done);
+          Account.findOne({ name: 'test' }, function(error, doc) {
+            assert.ifError(error);
+            assert.equal(doc.__v, 0);
+            db.close(done);
+          });
         });
+      });
   });
 
   it('works with nested schemas and $pull+$or (gh-1932)', function(done) {
diff --git a/test/model.populate.test.js b/test/model.populate.test.js
index 3338b0557b3..d907e87176b 100644
--- a/test/model.populate.test.js
+++ b/test/model.populate.test.js
@@ -3001,6 +3001,54 @@ describe('model: populate:', function() {
         done();
       });
     });
+
+    it('with nonexistant refPath (gh-4637)', function(done) {
+      var baseballSchema = mongoose.Schema({
+        seam: String
+      });
+      var Baseball = db.model('Baseball', baseballSchema);
+
+      var ballSchema = mongoose.Schema({
+        league: String,
+        kind: String,
+        ball: {
+          type: mongoose.Schema.Types.ObjectId,
+          refPath: 'balls.kind'
+        }
+      });
+
+      var basketSchema = mongoose.Schema({
+        balls: [ballSchema]
+      });
+      var Basket = db.model('Basket', basketSchema);
+
+      new Baseball({seam: 'yarn'}).
+        save().
+        then(function(baseball) {
+          return new Basket({
+            balls: [
+              {
+                league: 'MLB',
+                kind: 'Baseball',
+                ball: baseball._id
+              },
+              {
+                league: 'NBA'
+              }
+            ]
+          }).save();
+        }).
+        then(function(basket) {
+          return basket.populate('balls.ball').execPopulate();
+        }).
+        then(function(basket) {
+          assert.equal(basket.balls[0].ball.seam, 'yarn');
+          assert.ok(!basket.balls[1].kind);
+          assert.ok(!basket.balls[1].ball);
+          done();
+        }).
+        catch(done);
+    });
   });
 
   describe('leaves Documents within Mixed properties alone (gh-1471)', function() {
diff --git a/test/model.query.casting.test.js b/test/model.query.casting.test.js
index aeaf4903a02..421df199d03 100644
--- a/test/model.query.casting.test.js
+++ b/test/model.query.casting.test.js
@@ -965,6 +965,33 @@ describe('model query casting', function() {
     });
   });
 
+  it('date with $not + $type (gh-4632)', function(done) {
+    var db = start();
+
+    var MyModel = db.model('gh4632', { test: Date });
+
+    MyModel.find({ test: { $not: { $type: 9 } } }, function(error) {
+      assert.ifError(error);
+      done();
+    });
+  });
+
+  it('_id = 0 (gh-4610)', function(done) {
+    var db = start();
+
+    var MyModel = db.model('gh4610', { _id: Number });
+
+    MyModel.create({ _id: 0 }, function(error) {
+      assert.ifError(error);
+      MyModel.findById({ _id: 0 }, function(error, doc) {
+        assert.ifError(error);
+        assert.ok(doc);
+        assert.equal(doc._id, 0);
+        done();
+      });
+    });
+  });
+
   it('minDistance (gh-4197)', function(done) {
     var db = start();
 
diff --git a/test/model.update.test.js b/test/model.update.test.js
index 877341c27d3..9c026a5cff0 100644
--- a/test/model.update.test.js
+++ b/test/model.update.test.js
@@ -1664,6 +1664,40 @@ describe('model: update:', function() {
       });
     });
 
+    it('with single nested and transform (gh-4621)', function(done) {
+      var SubdocSchema = new Schema({
+        name: String
+      }, {
+        toObject: {
+          transform: function(doc, ret) {
+            ret.id = ret._id.toString();
+            delete ret._id;
+          }
+        }
+      });
+
+      var CollectionSchema = new Schema({
+        field2: SubdocSchema
+      });
+
+      var Collection = db.model('gh4621', CollectionSchema);
+
+      Collection.create({}, function(error, doc) {
+        assert.ifError(error);
+        var update = { 'field2': { name: 'test' } };
+        Collection.update({ _id: doc._id }, update, function(err) {
+          assert.ifError(err);
+          Collection.collection.findOne({ _id: doc._id }, function(err, doc) {
+            assert.ifError(err);
+            assert.ok(doc.field2._id);
+            assert.ok(!doc.field2.id);
+            done();
+          });
+        });
+      });
+
+    });
+
     it('works with buffers (gh-3496)', function(done) {
       var Schema = mongoose.Schema({myBufferField: Buffer});
       var Model = db.model('gh3496', Schema);
@@ -1981,6 +2015,51 @@ describe('model: update:', function() {
       });
     });
 
+    it('push with timestamps (gh-4514)', function(done) {
+      var sampleSchema = new mongoose.Schema({
+        sampleArray: [{
+          values: [String]
+        }]
+      }, { timestamps: true });
+
+      var sampleModel = db.model('gh4514', sampleSchema);
+      var newRecord = new sampleModel({
+        sampleArray: [{ values: ['record1'] }]
+      });
+
+      newRecord.save(function(err) {
+        assert.ifError(err);
+        sampleModel.update({ 'sampleArray.values': 'record1' }, {
+          $push: { 'sampleArray.$.values': 'another record' }
+        },
+        { runValidators: true },
+        function(err) {
+          assert.ifError(err);
+          done();
+        });
+      });
+    });
+
+    it('update with buffer and exec (gh-4609)', function(done) {
+      var arrSchema = new Schema({
+        ip: mongoose.SchemaTypes.Buffer
+      });
+      var schema = new Schema({
+        arr: [arrSchema]
+      });
+
+      var M = db.model('gh4609', schema);
+
+      var m = new M({ arr: [{ ip: new Buffer(1) }] });
+      m.save(function(error, m) {
+        assert.ifError(error);
+        m.update({ $push: { arr: { ip: new Buffer(1) } } }).exec(function(error) {
+          assert.ifError(error);
+          done();
+        });
+      });
+    });
+
     it('update handles casting with mongoose-long (gh-4283)', function(done) {
       require('mongoose-long')(mongoose);