Issue with Drag&Drop in ListBox

[Haidong]

I use below code to create two list box and drag&drop listboxitem between this two list.
Sometimes it works well. But sometime when I drag item from list1 to list2, the item can not be drop to the list2. The item go back to the list1.
Please notice that I use Data template for the listboxitem and the data template is a little complex.

Could someone help me on that?

<Style TargetType="ListBoxItem"
              x:Key="draggableItemStyle">
           <Setter Property="telerik:DragDropManager.AllowDrag"
                   Value="True" />
           <Setter Property="telerik:DragDropManager.AllowCapturedDrag"
                   Value="True" />
       </Style>


<ListBox x:Name="MUL"

                             ItemsSource="{Binding List1, Mode=TwoWay}"

                             ItemContainerStyle="{StaticResource draggableItemStyle}"

                             AllowDrop="True"

                             Margin="10"

                             BorderBrush="{StaticResource BorderColor}">

                        <ListBox.ItemsPanel>

                            <ItemsPanelTemplate>

                                <controlsToolkit:WrapPanel Orientation="Horizontal"

                                                           Background="Transparent" />

                            </ItemsPanelTemplate>

                        </ListBox.ItemsPanel>

                        <ListBox.Template>

                            <ControlTemplate TargetType="ListBox">

                                <ScrollViewer HorizontalScrollBarVisibility="Disabled"

                                              VerticalScrollBarVisibility="auto"

                                              BorderThickness="0">

                                    <Grid Background="Transparent">

                                        <Border>

                                            <ItemsPresenter />

                                        </Border>

                                    </Grid>

                                </ScrollViewer>

                            </ControlTemplate>

                        </ListBox.Template>

                        <ListBox.ItemTemplate>

                            <DataTemplate>

                                  .......................

                            </DataTemplate>

                        </ListBox.ItemTemplate>

                        <telerik:ListBoxDragDrop.Behavior>

                            <telerik:ListBoxDragDropBehavior />

                        </telerik:ListBoxDragDrop.Behavior>

                        <telerik:ListBoxDragDrop.DragVisualProvider>

                            <telerik:ScreenshotDragVisualProvider />

                        </telerik:ListBoxDragDrop.DragVisualProvider>

                    </ListBox>