Everyone expects Combobox::setText to select the item in the listbox.
CE, you've already confirmed the bug on IRC.
user: Paul Turner <firstname.lastname@example.org>
date: Wed Feb 29 10:36:25 2012 +0000
summary: FIX: Combobox was not setting list items as selected in some scenarios involving setting the editbox text, where it would be the expected behaviour for a matching list item to be marked as selected.