I have an InformationLayer that contains points through a LocationCollection property in a view model. When I call the Clear() method on the LocationCollection, the lines on the map don't go away (even if I zoom in or out). My InformationLayer XAML looks like the following. As mentioned, MyPolyline is a LocationCollection:
It appears I'm running version 2011.2.920.40. I have confirmed the MyPolyline.Count property is 0 after calling the Clear() method, but as mentioned, the lines on the map don't go away.