title: DataGridComboBoxColumn does not display SelectedItem
body: <p>I have a ViewModel (pseudo code for its structure):</p>
  
  <pre><code>class ViewModel
  {
      public List&lt;Package&gt; Packages { get; set; }
  }
  enum Type
  {
      Type1,
      Type2, ....
  }
  class Package
  {
      public Type PackageType { get; set; }
  }
  </code></pre>
  
  <p>This is how I bind my DataGrid with the property Packages of the ViewModel.</p>
  
  <pre><code>&lt;DataGrid ItemsSource="{Binding Packages}"&gt;
          &lt;DataGrid.Columns&gt;
              &lt;DataGridComboBoxColumn ItemsSource="{Binding Source={StaticResource Types}}"
                                      SelectedItemBinding="{Binding PackageType, Mode=TwoWay}"&gt;
              &lt;/DataGridComboBoxColumn&gt;
          &lt;/DataGrid.Columns&gt;
  </code></pre>
  
  <p>This is how I define Resource Types:</p>
  
  <pre><code>&lt;Window.Resources&gt;
      &lt;CollectionViewSource x:Key="Types"&gt;
          &lt;CollectionViewSource.Source&gt;
              &lt;ObjectDataProvider MethodName="GetNames" ObjectType="{x:Type sys:Enum}"&gt;
                  &lt;ObjectDataProvider.MethodParameters&gt;
                      &lt;x:Type TypeName="s:Type"/&gt;
                  &lt;/ObjectDataProvider.MethodParameters&gt;
              &lt;/ObjectDataProvider&gt;
          &lt;/CollectionViewSource.Source&gt;
      &lt;/CollectionViewSource&gt;
  &lt;/Window.Resources&gt;
  </code></pre>
  
  <p>DataGridComboBoxColumn can show the ComboBox. However, it does not show the value of the Package.PackageType. It behaves like the binding is only one way to source. When I update the ComboBox, the object is updated. The other way does not work.</p>
  
  <p>Please help. Thanks a lot.</p>