THE BUG

If a double chest with items in the 4th,5th,6th row is cloned, the game will stop saveing, and you will be in a ghost state like you just exploded a LOT of tnt. the game will not close, but you can't do anything from that point that affects the game or the savefile. 

WHAT I KNOW

This bug is related to the fact that when a double chest is cloned it will first place down two normal chests and then try to make dose two into a double chest. But as you know, a chest with items normally doesn't turn into a double chest when it is placed next to another chest(only in creative. by pressing ctrl while pick-blocking).

So the game can't make the two cloned chests into a double chest. And that will 'crash'(ghost state)the game.