Partial updates of non-opque QGraphicsItems blended with old content, if cached mode is enabled

A QGraphicsItem is using setCacheMode(QGraphicsItem::ItemCoordinateCache). When item invalidates only partial region, its updated region gets painted on top of the old content. If the item is non-opaque, the old content is shown below the newly painted content.

Below might be the cause of the bug:

qgraphicsscene.cpp, line4286

if (!subPix.isNull())

{ // Blit the subpixmap into the main pixmap. pixmapPainter.begin(pix); // HERE painter should be in "Source" composition mode, not the default SourceOver pixmapPainter.setClipRegion(pixmapExposed); pixmapPainter.drawPixmap(br.topLeft(), subPix); pixmapPainter.end(); }

Eg. QPainter composition mode should be "QPainter::CompositionMode_Source" in the if -branch:
http://qt.gitorious.org/qt/qt/blobs/master/src/gui/graphicsview/qgraphicsscene.cpp#line4286