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:
Use /spawnpoint in the End
Kill yourself or jump into the end portal
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.
Confirmed. You can also get your screen stuck when you subsequently enter the exit portal. Enter the exit portal more than once to exist in the End, blinded and paralyzed by a loading screen (though you can still hear end music and enderman noises).
Edit: also if an enderman walks into your center of view, it will get provoked and kill you, and remove the loading screen. This is one of the weirdest bugs ever!