GetTemplateChild Issue- SLBeta2

Here is another one of those things that might have changed in Beta2. I am not sure what/how should be changed as this was working in Beta1

Sometimes I get the following error

and sometimes Object Reference set to null, I was able to narrow it down to GetTemplateChild in OnApplyTemplate. All the calls to this method return null.

 public override void OnApplyTemplate()
        {
            base.OnApplyTemplate();
            _dropDownButton = GetTemplateChild(”ButtonElement”) as Button;
         _cp = GetTemplateChild(”ContentSite”) as ContentPresenter;
         _border = GetTemplateChild(”border”) as Border;
         _border.Visibility = Visibility.Collapsed          
            _cp.ContentTemplate = ItemTemplate;
            if (_dropDownButton != null)
            {
                _dropDownButton.MouseLeftButtonDown += new MouseButtonEventHandler(_dropDownButton_MouseLeftButtonDown);
                _dropDownButton.IsTabStop = false;
            }
            _rootGrid = GetTemplateChild(”RootElement”) as Grid;            if (_rootGrid != null)           
                _rootGrid.SizeChanged += new SizeChangedEventHandler(RootGrid_SizeChanged);
                     
        }  

Here is the source

Please leave a comment of any solutions/workarounds

Update: Adding DefaultStyleKey=typeof(ComboBox) and DefaultStyleKey=typeof(ComboBoxItem) in the respective Constructors should solve this issue. this is New in Beta2

But I still cant get it to work, I get another exception

Update: If we replace ContentPresenter in ControlTemplates with ContentControl all is good and the issue is resolved (This is workaround for a known bug)