Unfortunately your observations are correct and we must admit we are aware of this problem. Our developers investigated the issue locally and it seems the current implementation of the numeric control does not work seamlessly in Silverlight. While we believe the problem is not related to the control itself but the Silverlight memory handling logic, we are currently redesigning the control to work around the problem and we believe we will be able to release a fixed version for the Q1 2009 release in February.
the Telerik team
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