title: ContextMenu commands on DataGrid Row do not work
body: <p>I create a style than I bind it to a <code>DataGrid.RowStyle</code> <code>Row</code> style. The <code>ContextMenu</code> appears and I am able to select from the menu items, but the <strong>command</strong> won't execute. I tested the <strong>command</strong> with other control and works fine. </p>
  
  <pre><code>&lt;Style x:Key="DataGridRow"  TargetType="{x:Type DataGridRow}"&gt;
       &lt;Setter Property="ContextMenu"&gt;
           &lt;Setter.Value&gt;
                &lt;ContextMenu DataContext="{Binding PlacementTarget.DataContext, RelativeSource={RelativeSource Self}}"&gt;
                      &lt;MenuItem Header="Add" Command="{Binding AddMessageContextMenu_Command}"/&gt;
                      &lt;MenuItem Header="Edit" Command="{Binding EditMessage_Command}"/&gt;
                &lt;/ContextMenu&gt;
             &lt;/Setter.Value&gt;
       &lt;/Setter&gt;
  &lt;Style&gt;
  
  &lt;DataGrid Name="SearchTableDataGrid" ItemsSource="{Binding SearchTableDataGrid_ItemSource}"
     &lt;DataGrid.RowStyle&gt;
       &lt;Style TargetType="{x:Type DataGridRow}"&gt;
            &lt;Style.Triggers&gt;
               &lt;Trigger Property="AlternationIndex" Value="0"&gt;
                     &lt;Setter Property="Background" Value="#FBFCFC" /&gt;
                &lt;/Trigger&gt;
                &lt;Trigger Property="AlternationIndex" Value="1"&gt;
                     &lt;Setter Property="Background" Value="#f6f8f8" /&gt;
                &lt;/Trigger&gt;
            &lt;/Style.Triggers&gt;
        &lt;/Style&gt;
     &lt;/DataGrid.RowStyle&gt;
  &lt;/DataGrid&gt;
  </code></pre>