I played on a server with a friend in the newest snapshot (13w19a) and I realized that you can't see if others change the item in their hand until you rejoin. You only see the item they had in their hand at the time you joined the server.
Hope you can fix it! Good Luck! 😉
Possseidon
23rd Duplicate of MC-14220, please use the search function to see if your bug has already been submitted. Currently over 56% of tickets are being closed as duplicate.