I've got a small but really annoying problem on my server. Whenever someone logs out and logs back in, he/she spawns at a place that is neither the spawn or the place he/she was at when logging out. Also the inventories of those persons are getting reverted to a state before this started happening.
I've tried restarting the server several times, didn't help.
Running version 3.1.2. Additional installed plugins are Dynmap, MobileAdmin, MineBackup and WorldEdit.
EDIT: Managed to fix it. Seemed to be some problem with the .dat files of the players.