Accelerated composited layers does not render correctly in HiDPI mode

Mac: When a webpage has something that triggers hardware acceleration then it does not display at the right size on a retina display. In the example attached two divs of 250x250 are displayed. On a normal display both are displayed correctly, but on a retina display the one on the left (which has -webkit:scale3d(1,1,1) set to trigger the hardware acceleration aspect).

One thing to note in the example is that a QGLWidget is used as a QGraphicsView viewport, commenting out this line still shows a problem but in a different way, but it seems possible that the QGraphicsView is also an influence in this.