Use multi-prop observer; default selected to null.

@@ -74,7 +74,7 @@
        */
       items: {
         type: Array,
-        observer: '_resetSelection'
+        notify: true
       },
 
       /**
@@ -100,11 +100,15 @@
        */
       multi: {
         type: Boolean,
-        observer: '_resetSelection'
+        value: false
       }
     },
 
-    _resetSelection: function() {
+    observers: [
+      '_resetSelection(items, multi)'
+    ],
+
+    _resetSelection: function(items, multi) {
       // Unbind previous selection
       if (Array.isArray(this.selected)) {
         for (var i=0; i<this.selected.length; i++) {
@@ -114,7 +118,7 @@
         this.unlinkPaths('selected');
       }
       // Initialize selection
-      if (this.multi) {
+      if (multi && items) {
         this.selected = [];
       } else {
         this.selected = null;

@@ -82,7 +82,7 @@
 
   test('bound defaults', function() {
     assert.equal(bind.$.observer.singleSelected, null);
-    assert.sameMembers(bind.$.observer.multiSelected, []);
+    assert.equal(bind.$.observer.multiSelected, null);
     bind.items = [
       {name: 'one'},
       {name: 'two'},