Tried to add entity with duplicate UUID

How to reproduce:
1. Start up fresh SMP server.
2. Profit

02.08 20:54:48 [Server] Server thread/WARN Tried to add entity with duplicate UUID 63e02e67-b1f7-4b46-a700-4c7ae1b78440
02.08 20:54:48 [Server] Server thread/WARN Tried to add entity with duplicate UUID 6c1e0ac0-87d8-4534-8f84-3b7b83d63e2c
02.08 20:54:48 [Server] Server thread/WARN Tried to add entity with duplicate UUID 74721ff9-7fa8-4b18-a6c8-d20ab159375e
02.08 20:54:48 [Server] Server thread/WARN Tried to add entity with duplicate UUID 64d1e74f-dfa6-48c1-90de-4bb593224e3b
02.08 20:54:48 [Server] Server thread/WARN Tried to add entity with duplicate UUID edeab727-b87f-4817-8a8e-ca78e0e3207f
02.08 20:54:48 [Server] Server thread/WARN Tried to add entity with duplicate UUID c1f8c40e-eaa8-46a2-9d16-4f4ebc760b69
02.08 20:54:48 [Server] Server thread/WARN Tried to add entity with duplicate UUID 969ff6b0-8d75-44b2-bc61-4df8a87bc014
02.08 20:54:48 [Server] Server thread/WARN Tried to add entity with duplicate UUID 84571e5a-043f-4912-bf15-3776b3673148
02.08 20:54:48 [Server] Server thread/WARN Tried to add entity with duplicate UUID 7a0beacd-7b1b-4c05-ba9b-82a08fda3f23
02.08 20:54:48 [Server] Server thread/WARN Tried to add entity with duplicate UUID fe7cfaac-c405-4b7e-9f6d-b12474c04b4b