[SMP] Items on hotbar of other player do not change visualy

Put the summary of the bug you're having here

What I expected to happen was...:
The item my friend is holding should change.

What actually happened was...:
The item in his hand stays the same a the one he was holding when he joined.

Steps to Reproduce:
1. Join a server and get 2 items on your hotbar.
2. Leave the server with Item A selected.
3. Join the server after a friend joined and then switch to Item B.
4. Look at his screen and you will see it still remains to be Item A.