Combo box within a group

Has anyone else had any problems trying to populate a combo box from a list object when the combo box is within a group?

I can't get it to work. I can create an identical combo box outside of a group, assign its input data to the same list object, and it populates fine.

This is rather frustrating as it's something I've encountered only because I'm trying to work around another issue (not being able to set the default item in a combo box)!