After playing for some while, I’ve noticed I can no longer interact with NPCs (it was shortly after opening treasure chest).
So I did only sane thing I could thing of and ran the client through a debugger. As it turns out, there seems to be memory corruption problem going on in that it sometimes corrupt part of memory that contains code for handling controls. I don’t know which exact function is an issue, but if I were you, I’d check all memcpy’s as they’re usually the culprit in such cases.