title: DataTemplate in ControlTemplate not updating Binding
body: <p>I've created a control with 3 PART_s, one PART_ changes depending on the type bound to it, however values changed within the Control do not update the Binding, it seems to work as OneWay Binding.</p>
  
  <p>Here's part of the code I beleive is relevant:</p>
  
  <pre><code>&lt;DataTemplate x:Key="BooleanDAView" DataType="{x:Type sys:Boolean}"&gt;
      &lt;CheckBox IsChecked="{Binding ., Mode=TwoWay}"/&gt;
  &lt;/DataTemplate&gt;
  &lt;DataTemplate x:Key="DateTimeDAView" DataType="{x:Type sys:DateTime}"&gt;
      &lt;extToolkit:DateTimePicker Value="{Binding ., Mode=TwoWay}"/&gt;
  &lt;/DataTemplate&gt;
  &lt;DataTemplate x:Key="Int32DAView"  DataType="{x:Type sys:Int32}"&gt;
      &lt;extToolkit:IntegerUpDown Value="{Binding ., Mode=TwoWay}"/&gt;
  &lt;/DataTemplate&gt;
  &lt;DataTemplate x:Key="StringDAView"  DataType="{x:Type sys:String}"&gt;
      &lt;TextBox Text="{Binding ., Mode=TwoWay}"/&gt;
  &lt;/DataTemplate&gt;
  </code></pre>
  
  <p>....</p>
  
  <pre><code>&lt;ContentControl x:Name="PART_Content"
          Grid.Row="0" Grid.Column="1"
          Margin="{TemplateBinding Padding}"
          VerticalAlignment="Center"
          VerticalContentAlignment="Center"
          Content="{Binding Path=Content, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay}"
          &gt;
      &lt;ContentControl.ContentTemplateSelector&gt;
          &lt;controls:TypeBasedDataTemplateSelector&gt;
              &lt;controls:TypeBasedDataTemplateSelector.Templates&gt;
                  &lt;controls:TypedDictionary&gt;
                      &lt;sys:String x:Key="{x:Type sys:Boolean}"&gt;BooleanDAView&lt;/sys:String&gt;
                      &lt;sys:String x:Key="{x:Type sys:DateTime}"&gt;DateTimeDAView&lt;/sys:String&gt;
                      &lt;sys:String x:Key="{x:Type sys:Int32}"&gt;Int32DAView&lt;/sys:String&gt;
                      &lt;sys:String x:Key="{x:Type sys:String}"&gt;StringDAView&lt;/sys:String&gt;
                  &lt;/controls:TypedDictionary&gt;
              &lt;/controls:TypeBasedDataTemplateSelector.Templates&gt;
          &lt;/controls:TypeBasedDataTemplateSelector&gt;
      &lt;/ContentControl.ContentTemplateSelector&gt;
  &lt;/ContentControl&gt;
  </code></pre>
  
  <p>For Content I've also tried ... <code>RelativeSource={RelativeSource AncestorType=local:DABaseControl}</code> but no change.</p>
  
  <p>If the DataTemplate Binding use <code>"{Binding Path=Content, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay}"</code> the template doesn't change once set.</p>
  
  <p>Or is there a better way to do this?</p>
  
  <p>Thanks</p>