I am glad to inform you that the issue is fixed in the Q1 2009 SP1 release (2009.1.402) of RadControls for ASP.NET AJAX. You can get it from the Downloads section of your account on telerik.com and upgrade your version following the steps from here
The filter option "Contain" is replaced with the "Contains" option. The functionality remains the same.
the Telerik team
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