I'm sorry, version 2012.2.607 of theTelerik.Windows.Controls.DataVisualization assembly had compatibility issue with Silverlight 4 runtime. The issue has been fixed and fix is available in the latest internal build. In fact this problem was concerned to all controls of the DataVisualization assembly, not just to RadMap. So, this fix also solves the problem with RadMap.
the Telerik team
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