/// <summary>
/// Called when ContentTemplateProperty is invalidated on "d."
/// </summary>
private static void OnContentTemplateChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
ContentPresenter ctrl = (ContentPresenter)d;
ctrl._templateIsCurrent = false;
ctrl.OnContentTemplateChanged((DataTemplate)e.OldValue, (DataTemplate)e.NewValue);
}