I went into the end, defeated the dragon, left the end, and quit the world. When I went back in, I went back to the end and threw an enderpearl in the second portal that appears. After that, everything but the player froze. The endermen were still and didn't interact with me, the enderpearl didn't work anymore and neither did the portal. And when I tried to quit the world, Minecraft stopped responding.
https://www.dropbox.com/s/i21fbzmh54xtle0/fml-client-latest.log?dl=0

should be fixed in f76103f

Wrong issue