"Comparison method violates its general contract!" crash

[ThatAlecs]

Hello everyone,
I run a server on Beta 1.1_02 using Poseidon and this error happens when you log out in the Nether and then log in the server again:

This absolutely prevents the player from logging in the server until the server owner/admin deletes their player data file, which resets all their data and progress on the server
When you try to log in the server while in the Nether, Minecraft will hang and then crash after a few minutes.

The steps to reproduce this bug are very simple:

1. Run a Beta 1.1_02 server using Project Poseidon
2. Get to the Nether
3. Log out
4. Try to log back in

[Moresteck]

Not a server issue. Add -Djava.util.Arrays.useLegacyMergeSort=true to JVM arguments in your launcher, or also Betacraft launcher has this fixed by default

[ThatAlecs]

Thanks for the quick response. I'll make sure to tell my players that.