title: Specified Visual is already a child of another Visual or the root of a CompositionTarget
body: <p>WPF Visualizer
  Visual Tree 
  canvas</p>
  
  <p>canvas.Children.Add poly |> ignore</p>
  
  <p>Specified Visual is </p>
  
  <ol>
  <li>already a child of another Visual or </li>
  <li>the root of a CompositionTarget.</li>
  </ol>
  
  <p>Don't think it's 1), not sure what 2) is?</p>
  
  <p>Using Visual Studio 2010, F# 2.0, WPF, ... not XAML</p>