title: Trigger not working, when binding property to dependecyproperty
body: <p>I'm trying to set the color of a rectangle (WPF) with triggers, depending on a boolean DependencyProperty, which I am binding to the Tag property of the rectangle.</p>
  
  <p>I have the following code:</p>
  
  <pre><code> public partial class MainWindow : Window
   {
      public Boolean isAutoStart
      {
          get { return (Boolean)GetValue(isAutoStartProperty); }
          set { SetValue(isAutoStartProperty, value); }
      }
  
      public static readonly DependencyProperty isAutoStartProperty =
          DependencyProperty.Register("isAutoStart", typeof(Boolean),
          typeof(MainWindow), new PropertyMetadata(true));
  
      private void Window_Loaded(object sender, RoutedEventArgs e)
      {
         isAutoStart = false;
      }
   }
  </code></pre>
  
  <p>and in XAML:</p>
  
  <pre><code>&lt;Window.Resources&gt;
      &lt;Style x:Key="TriggerDark" TargetType="Rectangle"&gt;
          &lt;Setter Property="Fill" Value="Green" /&gt;
          &lt;Style.Triggers&gt;
              &lt;Trigger Property="Tag" Value="False"&gt;
                  &lt;Setter Property="Fill" Value="Red" /&gt;
              &lt;/Trigger&gt;
              &lt;Trigger Property="Tag" Value="True"&gt;
                  &lt;Setter Property="Fill" Value="Green" /&gt;
              &lt;/Trigger&gt;
          &lt;/Style.Triggers&gt;
      &lt;/Style&gt;
  
  &lt;/Window.Resources&gt;
  
  &lt;Rectangle Style="{StaticResource ResourceKey=TriggerDark}" Tag="{Binding Path=isAutoStart, UpdateSourceTrigger=PropertyChanged}"&gt;
  </code></pre>
  
  <p>If I hardcode "True" or "False" into the tag property of the rectangle, the triggers work correctly.
  And if I print the value of the tag property on runtime to console, the binding works, but the triggers do not fire.</p>
  
  <p>Any ideas what I am doing wrong?</p>
  
  <p>Thanks!</p>