Issue #246 -- never fire nested change events for the same model. The top-level one will do.

backbone.js

@@ -204,6 +204,10 @@
       // Check for changes of `id`.
       if (this.idAttribute in attrs) this.id = attrs[this.idAttribute];
 
+      // We're about to start triggering change events.
+      var alreadyChanging = this._changing;
+      this._changing = true;
+
       // Update attributes.
       for (var attr in attrs) {
         var val = attrs[attr];
@@ -216,7 +220,8 @@
       }
 
       // Fire the `"change"` event, if the model has been changed.
-      if (!options.silent && this._changed) this.change(options);
+      if (!alreadyChanging && !options.silent && this._changed) this.change(options);
+      this._changing = false;
       return this;
     },
 

test/model.js

@@ -370,4 +370,30 @@ $(document).ready(function() {
     notEqual(Child.prototype.instancePropDiff, undefined);
   });
 
+  test("Model: Nested change events don't clobber previous attributes", function() {
+    var A = Backbone.Model.extend({
+      initialize: function() {
+        this.bind("change:state", function(a, newState) {
+          equals(a.previous('state'), undefined);
+          equals(newState, 'hello');
+          // Fire a nested change event.
+          this.set({ other: "whatever" });
+        });
+      }
+    });
+
+    var B = Backbone.Model.extend({
+      initialize: function() {
+        this.get("a").bind("change:state", function(a, newState) {
+          equals(a.previous('state'), undefined);
+          equals(newState, 'hello');
+        });
+      }
+    });
+
+    a = new A();
+    b = new B({a: a});
+    a.set({state: 'hello'});
+  });
+
 });