(In reply to comment #8)
> The vsynced blit path for presentation is implemented by *stalling* GPU
> command processing. That's a big hammer, and might be related to your
> problems. You can skip this (at the cost of tearing in some cases) by
> disabling SwapBuffersWait. Have you tried that, just for testing?

No effect I'm afraid. Since this is a full screen application I assume it was
already using flipping and not blitting anyway?