title: DataTrigger sets the default value when the condition is false
body: <p>So here is my XAML:</p>
  
  <pre><code>&lt;Ellipse Height="100" Width="100" Margin="35,112,0,0" Name="ellipse1" Fill="Red"&gt;
          &lt;Ellipse.Style&gt;
              &lt;Style TargetType="Ellipse"&gt;
                  &lt;Style.Triggers&gt;
                      &lt;DataTrigger Binding="{Binding ElementName=checkBox1, Path=IsChecked}" Value="true"&gt;
                          &lt;Setter Property="Ellipse.Visibility" Value="Collapsed"&gt;&lt;/Setter&gt;
                      &lt;/DataTrigger&gt;
                  &lt;/Style.Triggers&gt;
              &lt;/Style&gt;
          &lt;/Ellipse.Style&gt;
      &lt;/Ellipse&gt;
      &lt;CheckBox Content="CheckBox" Height="16" Margin="42,79,168,166" Name="checkBox1" /&gt;
  </code></pre>
  
  <p>When the checkbox is checked, of course the ellipse disappears but when it's unchecked, it appears again, but i don't know why. This behavior is normal? Why this is happening?</p>