title: AvalonDock 2.0 editable header
body: <p>I'm using Avalondock version 2.0 and set into the header custom editable texbox control.
  But when I changed the header text, the message does not invoke to the 
  ViewModel(see at <code>&lt;Setter Property="Title" Value="{Binding Model.DataContext.Caption, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"</code>).
  What can I solve this?</p>
  
  <pre><code>    &lt;xcad:DockingManager Grid.Row="1" regions:RegionManager.RegionName="{x:Static   common:RegionNames.DesignerRegion}" 
                           Style="{DynamicResource CustomDockingManagerStyle}"&gt;
          &lt;xcad:DockingManager.DocumentHeaderTemplate&gt;
              &lt;DataTemplate&gt;
                  &lt;behaviors:EditableTextBlock x:Name="EditableTextBlock" 
                                               Text="{Binding Path=Title}"
                                               TextBoxBorderColor="#C34442"
                                               TextBlockForegroundColor="{DynamicResource AddButtonBackground}"
                                               TextBoxForegroundColor="#7B3A3A"
                                               TextBoxBackgroundColor="#FFF1E6"
                                               HorizontalAlignment="Stretch"
                                               VerticalAlignment="Center"/&gt;
              &lt;/DataTemplate&gt;
          &lt;/xcad:DockingManager.DocumentHeaderTemplate&gt;
          &lt;xcad:DockingManager.LayoutItemContainerStyleSelector&gt;
              &lt;avalonBehaviors:PanesStyleSelector &gt;
                  &lt;avalonBehaviors:PanesStyleSelector.DocumentsStyle&gt;
                      &lt;Style TargetType="{x:Type xcad:LayoutItem}"&gt;
                          &lt;Setter Property="Title" Value="{Binding Model.DataContext.Caption, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"/&gt;
                      &lt;/Style&gt;
                  &lt;/avalonBehaviors:PanesStyleSelector.DocumentsStyle&gt;   
              &lt;/avalonBehaviors:PanesStyleSelector&gt;
          &lt;/xcad:DockingManager.LayoutItemContainerStyleSelector&gt;
          &lt;xcad:LayoutRoot &gt;
              &lt;xcad:LayoutPanel &gt;
                  &lt;!--xcad:LayoutDocumentPaneGroup&gt;
                      &lt;xcad:LayoutDocumentPane /&gt;
                  &lt;/xcad:LayoutDocumentPaneGroup--&gt;
                  &lt;xcad:LayoutDocumentPane /&gt;
                  &lt;xcad:LayoutAnchorablePane DockWidth="250" &gt;
                      &lt;xcad:LayoutAnchorable Title="Properties" AutoHideWidth="250"&gt; 
                          &lt;ContentControl regions:RegionManager.RegionName="{x:Static common:RegionNames.PropertiesRegion}"/&gt;
                      &lt;/xcad:LayoutAnchorable&gt;
                  &lt;/xcad:LayoutAnchorablePane&gt;
              &lt;/xcad:LayoutPanel&gt;
              &lt;xcad:LayoutRoot.BottomSide&gt;
                  &lt;xcad:LayoutAnchorSide&gt;
                      &lt;xcad:LayoutAnchorGroup&gt;
                          &lt;xcad:LayoutAnchorable Title="Log Messages"&gt;
                              &lt;TextBox IsReadOnly="True" Text="{Binding LogMessage}" TextWrapping="Wrap" VerticalScrollBarVisibility="Auto"/&gt;
                          &lt;/xcad:LayoutAnchorable&gt;
                      &lt;/xcad:LayoutAnchorGroup&gt;
                  &lt;/xcad:LayoutAnchorSide&gt;
              &lt;/xcad:LayoutRoot.BottomSide&gt;
          &lt;/xcad:LayoutRoot&gt;
      &lt;/xcad:DockingManager&gt;
  </code></pre>
  
  <p>Thanks</p>