This seems to be related to the number of updates that are coming in from the GPS service. On each update received, there is a call to PanTo. I'm assuming that each successive call results in a cancellation of the previous request. The problem is that I never seem to get an updated view, as every update request to the map service will be cancelled by the next call. The more weird part is that if I turn off the location tracking (constant use of PanTo to center the map), the final PanTo command never results in a refresh/update/redraw of the map data until I move the map with the mouse.