The beam in RadComboBox in editable mode comes from the inner TextBox. The missing beam could come from several things - custom RadComboBox Style or implicit TextBox Style, that changes the inner TextBox colors, so the beam is not visible (or indistinguishable). Do the other TextBox controls on the same Window have the beam visible? Are their colors different than the RadComboBox?
All the best,
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items