World needs to set to creative(might happen in survival too), with the world type set to normal and cheats on.
First to /tp username 2999999 256 ~ (the y can be anything you like but I use 256 to be safe when in creative so I don't have to worry about spawning in blocks and talking my time to get back to the surface)
Now wait a few seconds.
You should get kick out of the world with the error of illegal position, this will also make the world unplayable without using 3rd party tools to move the players location.
MC-60905
World Boarder Bug illegal position
Resolved
Duplicate
0
pie595
(Unassigned)
Unconfirmed
Minecraft 14w27b
Retrieved
Searge's comment from MC-53433:
Since the farlands were removed many versions ago there is no real reason anymore to go so far away from spawn. As soon as a player manages to get there without using teleports or other cheat, we can reopen this ticket.