title: Visibility binding not working on initial start up
body: <p>I have 2 drop down gallery controls in my project. The choice of the first drop down is what controls what is shown in the second one. I have a couple categories and their visibility is controlled by the enum of the selected item. </p>
  
  <pre><code>&lt;RibbonGalleryCategory Header="Slice Attributes" Visibility="{Binding Path=MapModel.SelectedTypeKey, Mode=TwoWay, Converter={StaticResource EnumMatchToVisibilityConverter}, ConverterParameter={x:Static map1:TypeKey.Slice}}"&gt;
  </code></pre>
  
  <p>This works fine except on initial start up. If I change the first drop down the list filters as expected. It shows everything on initial star up and seems to ignore the visibility based on the first drop down. I am using MVVM so I would prefer to not use code behind if I can help it. </p>
  
  <p>Any ideas how I can get the filtering to work on initial start up?</p>