If a player logs into their world with a alt. account that account receives the same inventory as the previous account. I discovered this while playing LAN with my family, I noticed my stuff was duped over when I switched to a new account to play on.

   Say you have a world that you change accounts on, that newer account has all the previous items. The computer/world keeps track of what items the player has but it doesn't compensate for what account is used.