Player Duplication

This is most likely because of server lag.

Maybe, but how? I've allocated 2 gigs of Ram and there are at most 3 people around at a time.

here's the code i run when starting the server:

START "Server" /HIGH java.exe -Xms2048M -Xmx2048M -jar minecraft_server.14w31a.jar nogui

Would be a regression of MC-37586, please provide more informatio over there and request a reopen.