duplication glitch

There's a duplication glitch that allows people to duplicate items by moving a chest with a piston just as they take an item out. If they time it just right, (right as the repeater reaches the piston and right before the piston fires), it will duplicate the item as if the item stayed in the chest and was removed at the same time. There are videos on Youtube. I assumed this counted as an exploit, which is why I set it to Minecraft - Private.