Hi all,

I would like to let you know, that this behavior is by design. There is a difference between RadComboBox and RadDropDownList controls. 

RadComboBox control doesn't have selection of items - when an item is selected, its text goes to the input, but in the drop-down there is only a hover of the item(there is no selection). I made you a video showing how the RadComboBox behaves when you select an item: http://screencast.com/t/hkLeJs8sc5

RadDropDownList on the other side has a selection of the items in its drop-down. That is why the previously selected item remains selected, and you can highlight another item. In the following video you can see how this control behaves:
http://screencast.com/t/x5idZupXfgR

Regards,
Aneliya Petkova