It has happened again only this time it was with round guards, also it appears it happened with the normal guards as well. It doesn't make it unplayable it is just laggy if anything is dropped on to it moved within it (i.e. picking anything up from around it).
In 0.1.0 theres a bug where normal guards just appear (like 100s of them) it happens at seemingly random times. This is after I furnaced about a hundred.
