QPainter::drawImage draws images in different places depending on image format

When drawing two images of the same size in the same place, the images don't actually appear in the same place if one of them is premultiplied and the other isn't. I've attached a code sample to reproduce the issue. I've also attached a screenshot. I'm not sure why the scroll bars are messed up but I'm not concerned about that. The top image is not drawn in the same place as the bottom image. If the code sample is edited so that both images are the same format, the problem disappears.