Affects Version/s: Minecraft 1.7.9
Fix Version/s: None
My friend's network had some issues, when he reconnected, his old player still stayed in the game, he killed that player (his other character), and that dropped all the items he had, basically duplicating all his items.
1. Join a server
2. Kill your network
3. Reconnect to the server after fixing network (in short period of time)
4. Kill your other character