only check deepEqual when not new

all updates on new docs will be marked modified anyway

pref improvement

lib/document.js

@@ -200,7 +200,6 @@ Document.prototype.set = function (path, val, type) {
   }
 
   if ('string' !== typeof path) {
-
     if (null === path || undefined === path)
       return this.set(val, path);
 
@@ -268,17 +267,19 @@ Document.prototype.set = function (path, val, type) {
     if (!pathToMark) pathToMark = path;
   }
 
-  var markedModified = this.isDirectModified(pathToMark);
 
   if ((!schema || null === val || undefined === val) ||
     this.try(function(){
       val = schema.applySetters(schema.cast(val, self), self);
     })) {
 
-    var priorVal = this.get(path);
-
-    if (!markedModified && !deepEqual(val, priorVal)) {
+    if (this.isNew) {
       this._activePaths.modify(pathToMark);
+    } else {
+      var priorVal = this.get(path);
+      if (!this.isDirectModified(pathToMark) && !deepEqual(val, priorVal)) {
+        this._activePaths.modify(pathToMark);
+      }
     }
 
     for (var i = 0, l = parts.length; i < l; i++) {