We fixed similar problem in the past (I wasn't able to quickly find the specific version, though) and I believe that if you upgrade to the latest available version of RadControls under your account the problem will disappear. If it persists, please, send us a simple project that can be used to observe the problem and we will do our best to provide a fix with one of the upcoming internal builds or SP releases (you might need to upgrade, though).
the Telerik team
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