Did you rebuild the project before running? Probably the assemblies were not updated by Visual Studio? You may also try to re-add the references to the Telerik assemblies if the rebuild does not help. The correct assembly version of all Telerik assemblies is:
I am attaching a simple application that has two combo boxes, one data-bound and one with static items. It demonstrates the bug we fixed. Please, let me know if your problem is different.
the Telerik team