I was playing aronund in snapshot in creative when that happend.

I pressed F to have an item in my off-hand, and it duplicated itself. Then i threw away the same item in my normal hand, and ended up with a stack of 0 items in my off-hand. If i were to pick it up in my inventory, it vanished. Then I got another item and swapped it with 0 stack one, so 0 stack item was in my main hand. After that i opened the chest, and game crashed. Works with any item.