I get either more or less concrete if it is put in water concentrate powder break fast enough

What I expected to happen was...:
let's say I have 10 white concentrate powder and 10 black concentrate powder how much should I get? Of course this is the same amount

What actually happened was...:
why do I get for example 6 white concrete and 11 black?!

Steps to Reproduce:
1. Let's build the simplest concrete structure we can think of. Let it be dug 2 blocks deep, a water source and a sign at the beginning (see the screen)
2. take the concentrate powder in your left hand and the diamond pick in your right
3. let's start putting concentrate powder and immediately break it. Oh, we're not getting the amount we expected