Window Modal dialogs are broken on OS X when QGLWidget is in hierarchy

If you have a QGLWidget within a window's hierarchy, and then attempt to open a WindowModal dialog, it causes two problems:
1. It shows as application modal dialog.
2. After closing it, you can't access menu items, like Quit.

This works in Qt4.8.

Alternatively, you can work around the problem by always using the window widget as the modal dialog parent. But this was not previously required.

For example, if you are in some child widget code and write this:
QMessageBox * box = new QMessageBox(this);
msgBox->setWindowModality(Qt::WindowModal);
msgBox->show();
... it will cause the described error

However, if you reference the window widget instead, it will work:
QMessageBox * box = new QMessageBox(window());