I'm encountering a bug in a WIP (using 2.06). I'm fairly certain it's something that I've heard of before, but I can't remember any details about what might be causing it, nor can I think of a decent term to search for.
The problem is in one particular room; there is a single triangle of shadow that seems to float in the player's vision. It is not affected by objects behind it; it appears to be floating in the air rather than being cast on surfaces like a normal shadow. It only happens when looking in one direction at one specific area. As the player moves, the triangle stays in the same spot on the screen, but gets smaller or larger as if it is getting closer or further away.
Does this sound familiar to anyone? I'd post a video, but it's happening inside a room that I don't want to reveal.