Item duplicating

Setup as following: A chest at the bottom, a hopper on top, a rail on to of the hopper, a minecart with hopper on top of the rail and a block on top of the rail and the minecart with hopper. Drop at least 39 items of the same type onto the block while standing on it. The player should get back a item. However, when all the items run through to the chest, there are still 39 items, causing a item duplicate bug.