I am not sure what is happening or what is going on, but when I trek across land I've already visited, Chunks that have already been created prior, there is an enormous lag spike that renders the game to 0 FPS. I log out and log back in and the framerate remains the same, but I am surrounded by countless numbers of mobs all around me. I try to enter creative mode and kill them, but no matter how many I kill they seem to continue spawning. So far, only two occurrences have happened, one with an explosion of Chickens and one with an explosion of Pigs. The only way to fix this, I have thus far found, is to use an editor program, MC edit and completely delete the affected chunk. After a new chunk is remade automatically the bug seems to stop, but still quite a few pigs remain. This seems to be more than a minor bug as it renders the game unplayable with extraordinary framerate drops.