Hmm, that's true.
Neither labelAttr or labelFunc work well w/ComboBox (or FilteringSelect). It's a design issue.
labelAttr and labelFunc mostly work to control what markup is displayed in the drop down list, but I think the <input> field needs to display the searchAttr because when the user blurs the ComboBox, then ComboBox tries to do a lookup based on that string in the <input>. But if the <input> field just displays the searchAttr then having a custom label isn't very useful.
So, not sure what to do about this ticket, maybe the ComboBox needs to have two states, marking whether the input contains a label or a search string.
Still, that doesn't allow rich text in the <input> field which is what I was really after in the first place w/this labelAttr/labelFunc feature.