When I go mining for diamonds, or any other ore, I usually dig tunnels. But for some reason, when I dig them I get far enough to where the world cuts off until you look back at it. But when you look back again, the bug is back. (happens again) It also happens in long caves.

I expected everything to go as I thought. No world cut-offs.

What actually happened was the world cut off.

1. Dig a tunnel or find a long cave,
2. Go far enough and either go in third person, or look to the right or left a bit,
3.There will be a HUGE cut off in the world until you look back far enough...

(the pictures I have provided straight from Minecraft, shows what the bug looks like)