When the backpack is placed on the ground, one player breaks the backpack and the other takes items out. When the backpack is broken the other players gui does not close even thought the backpack is not present.

Confirmed as of 1.0.20.20 on minecraft 1.12.2. You can emulate the "another player breaking the backpack" with a block breaker connected to a timer and still be able to dupe.

Fixed

Also please fix this asap.

Thanks!