Can't Lock Top Hopper for Sorting

I created a water stream sorting system for wool with locking hoppers and unlocked hoppers just like YouTuber Wattles made ... link: https://youtu.be/sQPyMxipAas

Where mine is not working correctly is the locked hoppers. When I put in 44 (stone slabs) placeholders and 1 color of the wool I want sorted this should lock the hopper. It does not. When I run wool down the water stream the locked hoppers randomly work but mostly don't work. My stone slabs get filtered out of the hopper and end up in the bottom chests and other colors of wool get put into the wrong color hopper as. well.

I have looked for an answer but can't find one. My design is correct and I even rebuilt the sorter just in case. The problem is most likely because I am using the Pocket Edition and he isn't, but I don't know the solution.

At some point, it would be awesome if a new hopper was designed... one that is an item specific, locking hopper where you only have to put in 1 of the item you want locked/sorted. This way it should work with all versions. 

Thanks in advance. 

Also, I don't know if I chose the correct affects version above... it's the only one that made sence. Wish there was a "I have no clue" option.