hopper duplication items

I was trying out the hopper with a with flowing water and a 64 stack of iron ore but it started to copy the block returning more then I through

blocks should be same number you throw out and collect with the hopper

a stack of 64 slowly dropped into a water conveyor into a hoppers connected to a chest causing a duplication

1. connect hopper to a chest
2. please 3 7 long rails of blocks in the from of a trough
3. put one water block on the end and let it flow over the hopper
4. drop items and watch

p.s. trough not needed