Transformation of QGraphicsProxyWidget doesn't work as expected

See the attached pictures. In button1.png a z-Rotation of the blue button doesn't fit the red bounding rect. It works correctly for the QGraphicsRect below. Even worse: rotating results in artifacts (see button2.png). An other example is graphtext.png: the embeded QPlainTextEdit is bigger than the bounding rect. Again it works correctly for QSimpleGraphicsText below. I did not have this problem with prior Qt versions!!