Inserting a QOpenGLWidget causes a recreation of the top level window

When inserting a QOpenGLWidget the top level window becomes deleted and recreated. For the user it has not only a flicker effect - the new window is repositioned by the policy of the window manager for new windows ( in my case centered ).

The problem appears only once - any following insertion of QOpenGLWidgets work like expected.

The bug has been reported on the Qwt bug tracker ( https://sourceforge.net/p/qwt/bugs/358/ ) for X11 and Windows, but might be available on other platforms as well.

I checked the situation with a small demo application myself. Attached is the code and a related callstack.