Server - Disconnect when started riding a horse.

When trying to ride a horse you will disconnected by the server with this error:
Internal exception: java.lang.NullpointerExpection

Server with debug mode on gives this error:
[INFO] NameOfMcPlayer lost connection: disconnect.genericReason
[SEVERE] Reached end of stream

When trying to relog you ge this:
[SEVERE] Reached end of stream
[INFO] NameOfMcPlayer[/XX..XXX.XX:XXXXX] logged in with entity id 483 at (-483.9695693440997, 86.7000000178814, -159.6389418331227)

I hope you guys can fix this multiplayer bug.