Illustrator keeps changing HSB values - fix to this?

Hello,

I'm doing some colour studies for an identity system and I want to create different colours from the same hue.

The only thing I want to change is the value and brightness.

When I have my starting colour swatch (for example 90,60,70 in HSB) and edit the saturation or brightness, Illustrator will automatically recalculate this colour with a different hue and a different saturation and brightness than the ones I put in.

Seeing as how I just want to create desaturated and lighter/darker versions of the same hue this is sort of problematic.

Again the example (the numbers are also automatically get extra decimals, but to keep it simple I'm not dropping these in):

I start with 90, 60, 70

I enter 90, 60, 50 and it goes to 89, 59, 50

I enter 90, 60, 20 and it goes to 94, 48, 20

I enter 90, 10, 70 and it goes to 91, 9, 70

I enter 90, 100, 70 and it goes to 99, 72, 69