title: WPF Image Style Trigger - small issue
body: <p>i'm having a small issue with an style trigger on an image.  The trigger does change the source of the image, but when it does i lose the streght="fill" property.  I've also tried setting it in the trigger, but it seem to ignore it.  What am i missing here?</p>
  
  <pre><code>&lt;Image x:Name="xBackground" 
          Height="99.5" 
          Width="271" 
          Stretch="Fill"&gt;
                  &lt;Image.Style&gt;
                      &lt;Style TargetType="{x:Type Image}"&gt;
                          &lt;Setter Property="Source" Value="Green.png"  /&gt;
                          &lt;Style.Triggers&gt;
                              &lt;DataTrigger Binding="{Binding HasAlarm}" Value="true"&gt;
                  &lt;Setter Property="Source" Value="Red.png" /&gt;
                              &lt;/DataTrigger&gt;
                          &lt;/Style.Triggers&gt;
                      &lt;/Style&gt;
                  &lt;/Image.Style&gt;
              &lt;/Image&gt;
  </code></pre>