Worldspawn inside the ground.

If you were to load up a superflat redstone ready world, it would set the world spawn inside the ground and teleport you there when you first spawn. If you die though, you get teleported to the top-most point of the ground. I seen other reports like this, but they were already a Fixed status and were from 1.4 - 1.5 updates.

Heres the seed: -7847572816975276785