Scene object: QGraphicsProxyWidget with own background and QWidget(s) "inside"

Problem is shown on the attached video. If object is moving above the other, the track of object's background stays on the bottom object.

The problem has been discovered only on the retina display on mac.

We have discovered that flag QGraphicsView::FullViewportUpdate for the scene solves the problem. So we guess that maybe calculating of repainting area for retina has errors.