Mac OSX: Opening a context menu causes the menu bar to switch from the window menu to the default menu

When a context menu is opened, the menu bar switches from the window menu to the default (application-wide) menu. It remains at the default menu after the context menu is closed.

Clicking away from the window (to another application) and back restores the window menu.

The attached project demonstrates the problem. Right-click on the window to open a context menu and see the menu bar change. The attached project also provides a FixedContextMenu class which, substituted for QMenu, partially fixes the problem. (The menu bar switches to the default while the context menu is open, but switches back when the context menu closes.)

This worked fine in Qt 4.8.