It seems as if all players get kicked even if only one of them is above y = 30M (and even when he had logged out). I tested it on a LAN singleplayer world with multiple accounts. But singleplayer is just a local server, could that mean the exploit could be used in order to ban all players? That could be very bad for some servers (other exploits could be used to reproduce the bug, even with commands disabled), and they definitely need to fix it.
I don't know whether multiplayer servers save the player data in the same way that singleplayer does, though. That may need to be tested.
Ohad Parpara
It seems as if all players get kicked even if only one of them is above y = 30M (and even when he had logged out). I tested it on a LAN singleplayer world with multiple accounts. But singleplayer is just a local server, could that mean the exploit could be used in order to ban all players? That could be very bad for some servers (other exploits could be used to reproduce the bug, even with commands disabled), and they definitely need to fix it.
I don't know whether multiplayer servers save the player data in the same way that singleplayer does, though. That may need to be tested.