Drawing 2D graphics onto a QGLWidget causes visual corruptions and performance loss

Dear QT-developers,

I am an occasional developer of the Mixxx project (www.mixxx.org) which is a free, open source DJ software for OSX, Windows and Linux. We face the following:

To visualize a song or track, Mixxx displays a waveform by using a QGLWidget. More precisely, we draw 2D graphics onto a QGLWidget subclass, named WGLWaveformViewer. This class is implemented in a way that it follows exactly the guidelines as mentioned in the QTGLWidget documentation.

Up to QT 4.5.3 the waveform widgets just worked fine on all operating systems, however, they now cause visual corruptions if compiling the project against QT 4.6.x. In detail, the visualization bug only affects Linux for QT 4.6.0, 4.6.1 and 4.6.2 - you can also reproduce the bug by simply executing the QT OpenGL examples on Linux while bringing another window to front.

QT 4.6.3 might have solved the problem on Linux according to the change-log. But on Windows (tested with XP (32bit) and 7(32bit) on different notebooks) it introduces massive visual corruptions that have not been seen in previous QT releases, see attached screenshots. The bug can be reproduced within a few minutes: Just get Mixxx from

https://code.launchpad.net/~mixxxdevelopers/mixxx/release-1.8.x

and compile it against QT 4.6.3 or the prospective 4.7.0 beta1 on Windows. Start mixing a few tracks produces the problem.

We have always compiled Mixxx against the latest QT version in the past and we would like to continue on this. We gently appreciate any help to solve this problem.
Feel free to post any related questions here.
Thanks in advance!