We investigated the problem. It is indeed a bug. We will fix it for the forthcoming SP1 release due in two weeks. The problem appears only if the Combobox is NonEditable. So for now you can use this as a workaround -- just use Editable Combobox.
About the second issue - such feature is not implemented yet. For now when you press ZZ it searches for a word starting with ZZ and thus stay on the first match (first word with Z as I suppose you don't have entry starting with ZZ ). We have this feature on our planning list so you can expect it in feature releases.
Thank you for your post, I have updated your Telerik points.
All the best,
the Telerik team
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