title: checkbox not setting dependency property
body: <p>I have this <code>DependencyProperty</code>:</p>
  
  <pre><code>public bool ShowEntireHierarchyEx
  {
      get { return (bool)GetValue(ShowEntireHierarchyExProperty); }
      set { SetValue(ShowEntireHierarchyExProperty, value); }
  }
  
  public static readonly DependencyProperty ShowEntireHierarchyExProperty =
      DependencyProperty.Register("ShowEntireHierarchyEx", typeof(bool), typeof(CustomizeStatisticsStyleControl), new UIPropertyMetadata(false));
  </code></pre>
  
  <p>And I'm binding it to this <code>CheckBox</code> in XAML:</p>
  
  <pre><code>&lt;CheckBox Margin="16,5,0,0" x:Name="checkBoxHierarcy"
            IsChecked="{Binding ElementName=customizeStatisticsStyle, Path=ShowEntireHierarchyEx, Mode=TwoWay}"&gt;
      S_how entire gate hierarchy
  &lt;/CheckBox&gt;
  </code></pre>
  
  <p>But for some reason the <code>CheckBox</code> does not change the <code>ShowEntireHierarchy</code> property, but if the <code>ShowEntireHierarchy</code> property changes in code, the <code>CheckBox</code> does change. What am I missing here?</p>
  
  <p>Thanks!</p>