Using setUnifiedTitleAndToolBarOnMac in a QMainWindow with a QToolBar makes the application unusable

Creating a simple Mac app (see attached code) with a QMainWindow that sets setUnifiedTitleAndToolBarOnMac to true and adds a QToolBar makes the QMainWindow widgets (except the top tool bar) insensitive. Undocking the toolbar solves the problem.

This bug makes any Mac app under 4.8.X unusable.