It happens during battles in the first area, somewhere near the first stairs. I can finish the battle, but it doesn't seem to do anything to fix it.
Frustratingly enough, it didn't happen now that I've saved the game several times and fought every enemy in the room. Not the first time I run into weird, one-off issues that can't be recreated- and after reporting it too, no less! Wouldn't surprise me if it only happens when you don't save since I had to start over three times because of it or something incredibly specific. Man, I'm pissed.
Just my luck to find weird, stupid, one-off issues that can't be recreated. Hell, there was that one time I tried to play a fangame and plugging in my controller disabled the framerate limiter. Sorry if this was a waste of your time...