Incredibly easy duplication glitch.

You can easily duplicate items by moving a chest with a piston, and taking the item a few frames before the piston moves, this can be in any way, a button, pressure plate, lever, anything. As long as the item is removed from the chest frames before the piston moves it, you will get a duplicated item. There are multiple ways to do this, so the only thing I could think of is changing how chests work with pistons.