title: WPF: Star in ColumnDefinition not expanding columns
body: <p>I have a user control that need the 1st and 3rd column to have the same width at all time.
  My code is a follows:</p>
  
  <pre><code>&lt;UserControl x:Class="UserControls.ListBoxSelector"
               xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
               xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"&gt;
      &lt;Grid&gt;
          &lt;Grid.ColumnDefinitions&gt;
              &lt;ColumnDefinition Width="5*" /&gt;
              &lt;ColumnDefinition Width="Auto" /&gt;
              &lt;ColumnDefinition Width="5*" /&gt;
          &lt;/Grid.ColumnDefinitions&gt;
          &lt;Grid.RowDefinitions&gt;
              &lt;RowDefinition Height="*" /&gt;
          &lt;/Grid.RowDefinitions&gt;
          &lt;ListBox x:Name="ListBox_Source" Grid.Column="0" Grid.Row="0" /&gt;
          &lt;StackPanel Grid.Column="1" Grid.Row="0" Orientation="Vertical"&gt;
              &lt;Button Content="&amp;gt;" Click="Button_Add_Click"/&gt;
              &lt;Button Content="&amp;lt;" Click="Button_Remove_Click" /&gt;
          &lt;/StackPanel&gt;
          &lt;ListBox x:Name="ListBox_Destination" Grid.Column="2" Grid.Row="0" /&gt;
      &lt;/Grid&gt;
  &lt;/UserControl&gt;
  </code></pre>
  
  <p>The result is not as expected as column 3 (ListBox_Destination) is not expanded at all. 
  Isn't the 5* in ColumnDefinition enough to force the 2 listbox to the same width??</p>
  
  <p>UPDATED : Sorry that I forgot to mention that the problem only occurs when I put the control inside a <b>RibbonGroup</b> using <b>Microsoft Ribbon for WPF</b></p>