The bug

Attempting to save a world with a world border center over 30 million blocks causes the player to be unable to respawn. The game crashes (Exception generating new chunk caused by java.lang.ArrayIndexOutOfBoundsException), and/or the world is corrupted (java.nio.channels.OverlappingFileLockException: null), and you become unable to open it again.

"Negative index in crash report handler (0/15)" is spammed to the debug log.

To reproduce

1. Create a new world.
2. Execute /worldborder center 50000000 50000000.
3. Execute /kill.
4. You are unable to respawn.
5. Attempt to go to title screen.
6. The game crashes, or the world becomes unable to be opened again.