[Solved] e.Options.Destination property always returns root item of the radtreeitem

[Xiaojun]

I drag an object from RadGridView to a RadTreeViewItem which includes dynamic items. It worked with 2011Q2 and SL4. Now it update to 2011Q3 and SL5. Then e.Options.Destination property always returns root item. And use the old version I can write "telerik:RadDragAndDropManager.AllowDrop="True"" in xaml file and it work. But now I must set RadDragAndDropManager.SetAllowDrop(d, true) in c# code.

<Grid x:Name="LayoutRoot" Background="White">
        <telerik:RadTreeView>
            <telerik:RadTreeViewItem>
...
            </telerik:RadTreeViewItem>
            <telerik:RadTreeViewItem Header=""
                                     ItemsSource="{Binding RootMailFolders,Mode=OneWay}"
                                     core:MailFolderDragAndDropManager.DropCommand="{Binding MoveMailToFolderCommand}"
                                     telerik:RadDragAndDropManager.AllowDrag="False"
                                     telerik:RadDragAndDropManager.AllowDrop="True">
                <telerik:RadContextMenu.ContextMenu>
                    ...
                </telerik:RadContextMenu.ContextMenu>
                <telerik:RadTreeViewItem.ItemTemplate>
                    <telerik:HierarchicalDataTemplate ItemsSource="{Binding Converter={StaticResource MailFolderConverter}, ConverterParameter={StaticResource ViewModelProxy}}">
                        <telerik:ContainerBinding.ContainerBindings>
                            <telerik:ContainerBindingCollection>
                                <telerik:ContainerBinding PropertyName="Command" Binding="{Binding DataContext.OpenMailFolderCommand, ElementName=LayoutRoot}" />
                                <telerik:ContainerBinding PropertyName="CommandParameter" Binding="{Binding}" />
                            </telerik:ContainerBindingCollection>
                        </telerik:ContainerBinding.ContainerBindings>
                        <StackPanel Orientation="Horizontal">
                            <Image
                                   Margin="0,0,5,0"/>
                            <TextBlock Text="{Binding FolderName,Mode=OneWay}" />
                        </StackPanel>
                    </telerik:HierarchicalDataTemplate>
                </telerik:RadTreeViewItem.ItemTemplate>
            </telerik:RadTreeViewItem>
        </telerik:RadTreeView>

public class MailFolderDragAndDropManager
   {
       public static readonly DependencyProperty DropCommandProperty = DependencyProperty.RegisterAttached("DropCommand",
           typeof(ICommand), typeof(MailFolderDragAndDropManager), new PropertyMetadata(null, OnDropCommandChanged));

       public static ICommand GetDropCommand(DependencyObject obj)
       {
           return (ICommand)obj.GetValue(DropCommandProperty);
       }

       public static void SetDropCommand(DependencyObject obj, ICommand value)
       {
           obj.SetValue(DropCommandProperty, value);
       }

       private static void OnDropCommandChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
       {
           if (e.NewValue != null)
           {
               RadDragAndDropManager.SetAllowDrop(d, true);
               RadDragAndDropManager.SetAllowDrag(d, true);
               RadDragAndDropManager.AddDragQueryHandler(d, OnDragQuery);
               RadDragAndDropManager.AddDropQueryHandler(d, OnDropQuery);
               RadDragAndDropManager.AddDropInfoHandler(d, OnDropInfo);
           }
           else
           {
               RadDragAndDropManager.SetAllowDrop(d, false);
               RadDragAndDropManager.SetAllowDrag(d, false);
               RadDragAndDropManager.RemoveDragQueryHandler(d, OnDragQuery);
               RadDragAndDropManager.RemoveDropQueryHandler(d, OnDropQuery);
               RadDragAndDropManager.RemoveDropInfoHandler(d, OnDropInfo);
           }
       }

       private static void OnDragQuery(object sender, DragDropQueryEventArgs e)
       {
           if (e.Options.Status == DragStatus.DragQuery)
           {
               if (e.Options.Source.DataContext != null && e.Options.Source.DataContext is MailHeaderDto)
               {
                   e.Options.Payload = e.Options.Source.DataContext;
                   e.Options.ArrowCue = RadDragAndDropManager.GenerateArrowCue();

                   ContentControl cue = new ContentControl();
                   cue.Content = ((MailHeaderDto)e.Options.Source.DataContext).Subject;
                   e.Options.DragCue = cue;
               }
           }

           e.QueryResult = e.Options.Payload != null;
           e.Handled = true;
       }

       private static void OnDropQuery(object sender, DragDropQueryEventArgs e)
       {
           if (e.Options.Status == DragStatus.DropDestinationQuery)
           {
               e.QueryResult = e.Options.Source != e.Options.Destination;
           }
           e.Handled = true;
       }

       private static void OnDropInfo(object sender, DragDropEventArgs e)
       {
           if (e.Options.Status == DragStatus.DropComplete)
           {
               ...//e.Options.Destination always return rootitem
           }
           e.Handled = true;
       }
   }

[Xiaojun]

Used ItemPrepared event of tree, it fixed. But I don't understand why 2011.Q2 could do that without adding these codes.