OpenGL widget not repainting correctly when placed in a child window. Mac OS X Carbon - regression

When having both an OpenGL subwindow and a regular widget subwindow in a QMdiArea, then the gl widget is not always repainting when the other subwindow is moved on top and off of it again.

This is a regression from Qt 4.5.3/Carbon.

Note: This is not supported in Cocoa due to limitations in the Cocoa API. (OpenGL widgets stack on top. This is also documented in the QGLWidget docs for Mac OS X)

This can be reproduced with the Qt mdi example.
Just replace mainwindow.cpp with the file attached. The only change is in the MainWindow constructor.
Run the examle and click "New file".