Those are absolutely a bug. They probably screwed up and didn't put mutexes around every piece of shared state.
"Some people wondered if the HUD textures are messed up in the optimized version, because the demo shows that as soon as you get hit by a monster the health and score numbers seem to blow up in your face. The answer is that this is part of the game play and already present in the original unoptimized version."
[1] http://www.vectorfabrics.com/blog/item/accelerating_the_idte...