Qt raster engine's drawEllipse produces polygons when used in drawBackground() of a scaled GraphicsView/Scene

Basic steps to reproduce is simply creating a QGraphicsScene with drawBackground overloaded, containing a drawEllipse call. When the corresponding QGraphicsView is scaled by a large amount, the circle produced will be a polygon with eight sides instead of a circle.
This problem only happens when the backend used is Qt's raster engine, which is the case by default on Windows. Confirmed to draw a perfect circle if used with either OS X or X backends.
In case the information is worth anything: I have tried to replicate this issue using a QPainter with the exact same transform() drawing on a plain QWidget with expected (good) results.
Simple example is attached.