QApplication::processEvents timing

[Zouch]

Hi guys,
We are using Qt for a visualization engine viewer, and we are having issues with the QApplication::processEvents() method.
Since we needed to control the framerate (in a game loop fashion), we overrided the QApplication to define our own and our game loop that looks like

MainApplication app;
// Some code here
while (true) {
    app.processEvents();
    app.doFrame();
    // sync code, nothing for now
}

This works fine, timing are about 0.001s for the processEvents() call, while, for an empty scene, the doFrame() takes about 0.0001s.
Now, we have a problem when we double click on title bar (to maximize the window). Indeed, after doing that, processEvents() call, goes from about 0.001s to about 0.01s (*10). Is this a known issue when using QtOpenGLWidget ? (most of the time seems to be taken in QPlatformBackingStore::composeAndFlush())

Thanks