title: wpf weird MenuItem visibility issue
body: <p>I have simple scenario in which i hide and show a signle <code>MenuItem</code> in a <code>ContextMenu</code> as shown below: </p>
  
  <p>Xaml: </p>
  
  <pre><code>&lt;Window x:Class="Window1"
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
          Title="Window1" Height="300" Width="300"&gt;
      &lt;Window.ContextMenu&gt;
          &lt;ContextMenu Name="mainMnu"&gt;
              &lt;MenuItem Name="mnu" Header="Testing"/&gt;
          &lt;/ContextMenu&gt;
      &lt;/Window.ContextMenu&gt;
  
      &lt;Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch"&gt;
          &lt;Button HorizontalAlignment="Left" Margin="52,131,0,108" Name="Button1"
                  Width="75"&gt;Button&lt;/Button&gt;
      &lt;/Grid&gt;
  &lt;/Window&gt;
  </code></pre>
  
  <p>code behind: </p>
  
  <pre><code>Private Sub Button1_Click(ByVal sender As System.Object,
                            ByVal e As System.Windows.RoutedEventArgs) Handles Button1.Click
      If mnu.Visibility = Windows.Visibility.Visible Then
          mnu.Visibility = Windows.Visibility.Collapsed
          mainMnu.Visibility = Windows.Visibility.Collapsed
      Else
          mnu.Visibility = Windows.Visibility.Visible
          mainMnu.Visibility = Windows.Visibility.Visible
      End If
  
  End Sub
  </code></pre>
  
  <p>The Problem is that every other time I press the <code>Button</code> the <code>MenuItem</code> is not shown. Right click only shows a small empty rectangle. (like there is a visible menu, but not a visible <code>MenuItem</code>). 
  It somehow works in a cycle... first 2 clicks: problem, next 2 clicks ok, and so on... </p>
  
  <p>Any ideas?</p>