dispensers in a row don´t suck in water properly

if there are dispensers in a row next to each other (tried 8 and 9) facing the same direction, with waterbuckets inside, when powered waterblocks will be placed properly but not sucked in as expected

What I expected to happen
when powering the row of dispensers with water in front of them and empty buckets insidde them, every waterblock gets sucked in and no water remains in front of the dispensers

What actually happened
at least one block of water remained in front of one dispenser and the bucked inside kept empty

Steps to Reproduce
1.) Put 9 dispensers in a row facing the same direction and provide them with waterbuckets.
2.) to power the dispensers, put a row of solid blocks above them and redstone on top.
3.) put a leaver ot button on one of the solid blocks above the dispansers.
4.) power them to place the water and then to suck the water in.