title: Error triggering animation based on boolean value
body: <p>Have a button that gets animated when a IsBusy boolean property on the ViewModel is True:</p>
  
  <pre><code>&lt;Button x:Name="button" Grid.Row="4"
          Command="{Binding QuitCommand}" 
          Content="{x:Static r:Resources.Close}" 
          RenderTransformOrigin="0.5,0.5"&gt;
      &lt;Button.Style&gt;
          &lt;Style TargetType="Button"&gt;
              &lt;Style.Triggers&gt;
                  &lt;DataTrigger Binding="{Binding IsBusy}" Value="True"&gt;
                      &lt;DataTrigger.EnterActions&gt;
                          &lt;BeginStoryboard Storyboard="{StaticResource TestStoryboard}"/&gt;
                      &lt;/DataTrigger.EnterActions&gt;
                  &lt;/DataTrigger&gt; **&lt;-- here is line 167 position 27**
              &lt;/Style.Triggers&gt;
          &lt;/Style&gt;
      &lt;/Button.Style&gt;
      &lt;Button.RenderTransform&gt;
          &lt;TransformGroup&gt;
              &lt;ScaleTransform/&gt;
              &lt;SkewTransform/&gt;
              &lt;RotateTransform/&gt;
              &lt;TranslateTransform/&gt;
          &lt;/TransformGroup&gt;
      &lt;/Button.RenderTransform&gt;
  &lt;/Button&gt;
  </code></pre>
  
  <p><strong>Storyboard:</strong></p>
  
  <pre><code>&lt;Window.Resources&gt;
      &lt;Storyboard x:Key="TestStoryboard"&gt;
          &lt;DoubleAnimationUsingKeyFrames 
          Storyboard.TargetProperty="(UIElement.RenderTransform).(TransformGroup.Children)[2].(RotateTransform.Angle)"&gt;
              &lt;EasingDoubleKeyFrame KeyTime="0:0:0.5" Value="25"/&gt;
              &lt;EasingDoubleKeyFrame KeyTime="0:0:1" Value="180"/&gt;
          &lt;/DoubleAnimationUsingKeyFrames&gt;
      &lt;/Storyboard&gt;
  &lt;/Window.Resources&gt;
  </code></pre>
  
  <p>If I initialize the IsBusy property to false and then launch the animation later, then everything works.  </p>
  
  <p>If I initialize the IsBusy property to true then I get the following errors:</p>
  
  <blockquote>
    <p>'[Unknown]' property does not point to a DependencyObject in path
    '(0).(1)[2].(2)'. 'Set property
    'System.Windows.FrameworkElement.Style' threw an exception.' Line
    number '167' and line position '27'.</p>
  </blockquote>
  
  <p><strong>ViewModel:</strong></p>
  
  <pre><code>public const string IsBusyPropertyName = "IsBusy";
  
  private bool _IsBusy = true;
  
  public bool IsBusy
  {
      get
      {
          return _IsBusy;
      }
  
      set
      {
          if (_IsBusy == value)
          {
              return;
          }
  
          RaisePropertyChanging(IsBusyPropertyName);
          _IsBusy = value;
          RaisePropertyChanged(IsBusyPropertyName);
      }
  }
  </code></pre>
  
  <p>Timing issue?</p>