title: Unable to delete a polygon on a bing Map Wpf control, cast exception
body: <p>I'm using the bing map wpf control.</p>
  
  <p>I add some polygon like this :</p>
  
  <pre><code>        polygon.Locations = DrawACircle(oLoc, dRadius);
          polygon.Tag = "Circle";
          MyMapUserControl.MyMap.Children.Add(polygon);
  </code></pre>
  
  <p>With this, my polygon are correctly displaying.</p>
  
  <p>Now, i would like to delete this polygon ( i can have severals polygon, that's why i use a tag : "Circle" ), i tried this :</p>
  
  <pre><code>var polygonToDelete = MyMapUserControl.MyMap
                                .Children
                                .OfType&lt;MapPolygon&gt;()
                                .Where(p =&gt; ((MapPolygon)p).Tag == "Circle");
  
  MyMapUserControl.MyMap.Children.Remove((UIElement)polygonToDelete);
  </code></pre>
  
  <p>I have an exception with a cast error.</p>
  
  <p>Anyone coud help me please ?</p>
  
  <p>Best regards,</p>