I have already answered to your question in the support ticket you have sent.
I will post the link that answers to your question in here also so the telerik community can take advantage of it: http://www.telerik.com/community/forums/aspnet-ajax/combobox/patch-ms-update-kb2586448-breaks-radcombobox-markfirstmatch-in-versions-older-than-2009-3-1314-inclusive.aspx
All the best,
the Telerik team
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