title: WP7 Silverlight Bing Map - MapPolyline doesn't zoom or move with map
body: <p>I added a MapPolyline to a Map control as follows:</p>
  
  <pre><code>&lt;Map&gt;
    &lt;MapLayer&gt;
      &lt;MapItemsControl&gt;
        &lt;MapPolyline Locations="{Binding locations}"/&gt;
  ...
  </code></pre>
  
  <p>This looks fine initially.  However, if I pan or zoom the map the MapPolyline doesn't move accordingly - it stays in the same place.  Is there something extra that needs to be done to link the MapPolyline to the current map location/zoom level?</p>