title: Expander collapse animation not work
body: <p>I have implement some animation on <code>Expander.Expanded</code> and this work fine, but similar one does not work on <code>Expander.Collapsed</code>. </p>
  
  <p>XAML:</p>
  
  <pre><code>&lt;Border Name="bor3" &gt;
     &lt;Border.Triggers&gt;
        &lt;EventTrigger RoutedEvent="Expander.Expanded" SourceName="exp3"&gt;
           &lt;EventTrigger.Actions&gt;
              &lt;BeginStoryboard&gt;
                 &lt;Storyboard&gt;
                    &lt;DoubleAnimation 
                       From="0" 
                       To="1" 
                       Duration="0:0:0.25" 
                       Storyboard.TargetName="gr3" 
                       Storyboard.TargetProperty="(FrameworkElement.LayoutTransform).(ScaleTransform.ScaleY)"/&gt;
                 &lt;/Storyboard&gt;
              &lt;/BeginStoryboard&gt;
           &lt;/EventTrigger.Actions&gt;
        &lt;/EventTrigger&gt;
        &lt;EventTrigger RoutedEvent="Expander.Collapsed" SourceName="exp3" &gt;
           &lt;EventTrigger.Actions&gt;
              &lt;BeginStoryboard&gt;
                 &lt;Storyboard&gt;
                    &lt;DoubleAnimation 
                       From="1" 
                       To="0" 
                       Duration="0:0:0.25" 
                       Storyboard.TargetName="gr3" 
                       Storyboard.TargetProperty="(FrameworkElement.LayoutTransform).(ScaleTransform.ScaleY)"/&gt;
                 &lt;/Storyboard&gt;
              &lt;/BeginStoryboard&gt;
           &lt;/EventTrigger.Actions&gt;
        &lt;/EventTrigger&gt;
     &lt;/Border.Triggers&gt;
     &lt;Expander Name="exp3"&gt;
        &lt;Grid Name="gr3"&gt;
           &lt;Grid.LayoutTransform&gt;
              &lt;ScaleTransform ScaleX="1" ScaleY="0"/&gt;
           &lt;/Grid.LayoutTransform&gt;
           &lt;TextBlock &gt;Test!&lt;/TextBlock&gt;
        &lt;/Grid&gt;
     &lt;/Expander&gt;
  &lt;/Border&gt;
  </code></pre>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>I've test <code>Datatriggers</code> beside control <code>Style</code> but that has a same problem:</p>
  
  <pre><code>&lt;Border Name="bor3" &gt;
      &lt;Expander Name="exp3"&gt;
          &lt;Grid Name="gr3"&gt;
              &lt;Grid.Style&gt;
                  &lt;Style TargetType="Grid"&gt;
                      &lt;Style.Triggers&gt;
                          &lt;DataTrigger Binding="{Binding IsExpanded, RelativeSource={RelativeSource AncestorType=Expander}}" Value="true"&gt;
                              &lt;DataTrigger.EnterActions&gt;
                                  &lt;BeginStoryboard&gt;
                                      &lt;Storyboard&gt;
                                          &lt;DoubleAnimation 
                                               From="0" 
                                               To="1" 
                                               Duration="0:0:0.25" 
                                               Storyboard.TargetProperty="(FrameworkElement.LayoutTransform).(ScaleTransform.ScaleY)"/&gt;
                                      &lt;/Storyboard&gt;
                                  &lt;/BeginStoryboard&gt;
                              &lt;/DataTrigger.EnterActions&gt;
                              &lt;DataTrigger.ExitActions&gt;
                                  &lt;BeginStoryboard&gt;
                                      &lt;Storyboard&gt;
                                          &lt;DoubleAnimation 
                                                  From="1" 
                                                  To="0" 
                                                  Duration="0:0:0.25" 
                                                  Storyboard.TargetProperty="(FrameworkElement.LayoutTransform).(ScaleTransform.ScaleY)"/&gt;
                                      &lt;/Storyboard&gt;
                                  &lt;/BeginStoryboard&gt;
                              &lt;/DataTrigger.ExitActions&gt;
                          &lt;/DataTrigger&gt;
                      &lt;/Style.Triggers&gt;
                  &lt;/Style&gt;
              &lt;/Grid.Style&gt;
              &lt;Grid.LayoutTransform&gt;
                  &lt;ScaleTransform ScaleX="1" ScaleY="0"/&gt;
              &lt;/Grid.LayoutTransform&gt;
              &lt;TextBlock &gt;Test!&lt;/TextBlock&gt;
          &lt;/Grid&gt;
      &lt;/Expander&gt;
  &lt;/Border&gt;
  </code></pre>
  
  <p>What is the problem and What is the solution?!</p>