Mobs in giant peices all around..

I was trying out a single player world on the 1.8 update, and saw a bunch of random things sticking out of the ground... I went into GM 3 to go into the ground and saw, like, parts of mobs or something everywhere..

Im not completely sure why this happened, but I have an profile with 1.7.2 forge loaded with some mods.

https://www.youtube.com/watch?v=0nZz0oMI7cs