More items going into a hopper than it can hold can duplicate the items

I drop 4x 64xFlower Pot and 1x 64x Anvil in a Hopper then I put on it and drop (ctrl + Q) 2x 64x Anvil on it,
after I have canceled automatically I'll throw them on it again (ctrl + Q)

when i set a slap on it a hopper i can't duplicate items with this trick.

PS:sry for google translater.