Horrible bug
While I'm playing, a (apparently) random chunk replaces all the chunks (air too), all the chunks become like the random chunk and the dimentions of the mobs increases a lot. This happens many many times if I turn around, while if I stay still it looks that chunks don't change. This makes the game unplayable and happens also if I reload the world. All the worlds I create until I close Minecraft have this bug. It disappares closing Mincraft and reloading it by the launcher. This bug is older than snapshot 15w41b. There was also in the snapshot 15w39c