title: No pushpin when using MapsTask on WP8
body: <p>I can't see the pushpin using MapsTask, the map is ok, but no pushpin on the map, anyone knows why? thank you!</p>
  
  <pre><code>        if (geo != null)
          {
              MapsTask mapsTask = new MapsTask();
              mapsTask.Center = geo;
              mapsTask.ZoomLevel = 15;
              mapsTask.Show();
          }
  </code></pre>