Hopper Duplication Glitch

Its a tricky duplication glitch to do, but it works. How to reproduce: Create a 9 block high tower, put a hopper 1 block below the tower, go to the top of the tower with the items you want to duplicate, look down to the hopper, save & quit your world, go back to the world you were just on, look down to the hopper, drop your items into the hopper, then count to 10, once you've counted to 10 close your game, finally go back to the world you were just on & observe the items in the hopper and you're inventory. This glitch works 75% of the time.