Cannot set spawnpoint in the nether or the end

The coordinates for the Nether + the Overworld are the same coordinates. The example is if you set a spawnpoint in the Nether then die, you're going to respawn at those same exact coordinates as you set in the Nether, but you spawn in the Overworld. This causes the player to re-do the adventure map from where they stopped at and NOT die, or just plain stop playing. This bug fix for an adventure map is extremely essential for players to SPAWN in the Nether, when facing a "Boss," or Powerful Mob, you should be able to spawn in the boss arena rather than having to go into the Nether again.

Steps to Reproduce:
1. Check your coordinates
2. Set a spawnpoint in the Nether
3. type /kill
4. Look at your coordinates and figure out what happened.