I have been playing on a LAN with my brother lately and it all worked fine for a while then I couldn't collect XP any more. By that I mean I can pick up the XP orbs and they make a sound and that's it, my XP bar does not go up.

1. We are both on 1.7.5 with Optifine
2. It worked for a while
3. We are playing on offline mode
4. We do have different accounts (Bought)
5. My brother's hosting and his XP works
6. Even using /xp doesn't work (E.g /xp 15L not working)
7. I have tried going on default resource pack, it's not the resource pack
8. Nothing works (E.g /xp, Killing Mobs, Mining.)
9. Problems that may be related: I can't open a chest after a while, Can't use item frames after a while, Can't see named mobs after a while, Can't use dogs after a while (This all happens after about 10 minutes of gameplay but not with XP)