GraphicsView painting regressions in master

We found a regression in the current graphicsview compared to the 4.5.2 one.
There are drawing artifacts when the graphicsview is scrolled,
and when either

• moving the scrollbars around, or
• doing a QPixmap::grabWidget on the graphicsview.

But there's a bug even without scrollbars: the final position of the animated
item is not always the same on screen. It looks like the final position
is not being drawn. The item is moved to the correct position, but the drawing
isn't uptodate.

Works with Qt-4.5.2 on Linux.
Fails with Qt-git-master from today on Linux, Mac and Windows.