I'm aware this is supposed to go in the bugbox, but it is currently down.
Suppose I wish to do a pixel-perfect upscale of a game (say 1px is rendered as 3px) I can do this ok in software and Direct3D 8, but there is a rendering bug in Direct3D 9. Something about the upscaling seems to stretch the image. Interestingly I noticed that this upscaling bug also happens for sub-applications but not when scaling sprites.
I've attached a simple reproduction to illustrate the issue. I have yet to come up with a suitable workaround.