Version 2009.1.527.35 does not support IE9 and you should consider migrating to a newer version of Telerik.Web.UI.dll released after the official release of IE9. Support for this browser was introduced in Q1 2011 (version 2011.1.315)
It is recommended to upgrade to the latest one which is Q2 2011 SP1, but if you have time you can wait for the official release of Q3 2011 scheduled for the middle of next week.
the Telerik team
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