Steps to reproduce crash:

1) Have hostile mobs kill you while you are standing inside a nether portal when you first enter the Nether.
Having a wall behind the Portal helps keep you inside the portal frame. (My portal spawned inside a Nether Fortress, against a wall. The mobs that killed me were zombies from the overworld.)

2) Once killed while in the portal, try to respawn. The respawn button does nothing. So click the title screen button.

3) Re-enter the world. Sometimes the game immediately kicks you out of the game and back to the game menu. If that happens, try to enter the world again.

4) Crash.

Note: Also happens in previous Minecraft versions. Other tested versions where bug occurs: 1.4.7