I have no idea if this is a bug or intended, but it literally makes the game unplayable so I'm reporting it anyway.

**Reproduction:

1. Use /spawnpoint in the End
2. Kill yourself or jump into the end portal
3. You respawn back in the End and cannot leave

And no, Nether Portals don't work in the End, meaing that there is no way out. Why is this relevant? Because it makes adventure maps that start in the End and then transition to another dimension impossible.