title: BitmapImage.ImageOpened Not Firing
body: <p>I am trying to download an image and have an event fire when it finishes. I use this:</p>
  
  <pre><code>BitmapImage btest = new BitmapImage(new Uri("http://www.google.com/images/srpr/logo4w.png"));
  btest.ImageOpened += btest_ImageOpened;
  
  void btest_ImageOpened(object sender, RoutedEventArgs e)
  {
      throw new NotImplementedException();
  }
  </code></pre>
  
  <p>However, the <code>ImageOpened</code> event will not fire. If I set an Image Control's source to the <code>BitmapImage</code> using:</p>
  
  <pre><code>image.Source = btest;
  </code></pre>
  
  <p>It does fire. Why doesn't the <code>ImageOpened</code> event fire unless the <code>BitmapImage</code> sender is set as an Image's source?</p>