title: Ember-data - isDirty is true after commit
body: <p>I'm trying to save a form on submit but discard changes in any other case. The problem is that even after a commit the isDirty flag is true.</p>
  
  <pre><code>App.UserController = Ember.Controller.extend({
      enterEditing: function() {
      this.transaction = App.store.transaction();
      this.transaction.add(this.get('content'));
    },
    updateEditing: function() {
      console.log('update saved');
      this.transaction.commit();
      this.transaction = null;
    }
  });
  App.UserView = Ember.View.extend({ 
      templateName: 'edit-user',
      willDestroyElement: function() {
      console.log(this.getPath('controller.content.isDirty'));
      if (this.getPath('controller.content.isDirty')) {
        console.log('unsaved changes');
        this.getPath('controller.content.transaction').rollback();   
      }     
    }
  });
  </code></pre>
  
  <p>And my router section:</p>
  
  <pre><code>showNew: Ember.Route.extend({
     route: '/user/new',
            cancelEditUser: Ember.Route.transitionTo('index'),
            connectOutlets: function(router) {
              router.get('applicationController').connectOutlet('user');
              router.get('userController').enterEditing();
            }
          }),
  
  
    update: function(router, event) {
      router.get('userController').updateEditing();
      router.transitionTo('index');
    }
  </code></pre>