Framerate drop

When I walked into a house in the game, my framerate severely dropped, and when I left it raised to a playable state again. It only happened in that one building. I have no clue where it was but it was somewhere near the centre of the map. It would be nice if this was fixed but I'm not sure how it would be.

I would bet if you messed around there long enough, you would be able to drop through the map, somewhere, somehow.