QGraphics*Item with setDashPattern gets corrupted while scrolling

I've attached a simple PyQt script to demonstrate this issue (sorry it's not C++).  Basically, I've got a QGraphicsRectItem (or other QGraphics*Item objects) which have a QPen with a dashPattern set, scrolling slowly around the QGraphicsView/QGraphicsScene will cause corruption in the newly-drawn areas of the item.  I've attached a picture to show what I mean - on my attached script, if you scroll slowly down, the lefthand side of the RectItem can be a nearly-solid line, whereas the righthand side won't get rendered at all.

This only seems to happen while scrolling.

I don't have an example handy but I've seen the exact same thing with QGraphicsLineItems as well.