title: Button IsEnabled Trigger does not work
body: <p>I have a <code>Button</code> and its Style:</p>
  
  <pre><code>&lt;Button Name="MyBtn" Style="{StaticResource ButtonEnabledStyle}"
          IsEnabled="False" Opacity="1" /&gt;
  
  &lt;Style x:Key="ButtonEnabledStyle" TargetType="Button"&gt;
      &lt;Style.Triggers&gt;
          &lt;Trigger Property="IsEnabled" Value="True" &gt;
              &lt;Setter Property="Opacity" Value="0.1" /&gt;
          &lt;/Trigger&gt;
      &lt;/Style.Triggers&gt;
  &lt;/Style&gt;
  </code></pre>
  
  <p>But when I enable the Button (<code>MyBtn.IsEnabled = true</code>) it does not change its Opacity. Why? How can I solve this problem? Thanks.</p>