QGraphicsView: negative scale transform breaks surrounding widgets in Mac OS X

QGraphicsView generates glitches in surrounding windgets in Mac OS X when negative scales are used to transform it.
The provided sample shows a QToolBox widget on the left side and a QGraphicsView on its right. That last widget has a negative scaling in Y axis using the following call:

ui->graphicsView->transform(QTransform().scale(1, -1));

which effectively flips the Y axis, but in Mac OS X this generates visual glitches on the QToolBox widget: tab separator lines dissapear randomly. Sample app launches maximized and perhaps with correct looking, but after changing QToolBox's tabs their lines dissapear. Even if I show a dialog with a QToolBox widget on it (not provided in sample program), those glitches are still visible. That is, somewhat scale QGraphicsView affects the QToolBox widget of the dialog.

That bug only happens in Mac OS X. On Windows XP, Windows 7 and Linux Ubuntu sample application runs perfectly. If I use QTabWidget instead of QToolBox there are still some glitches, also if I flip X axis instead of Y.

If I use QGLWidget to draw QGraphicsView this bug does not happen, so must be something related to software rasterization.