See video. I'm a software tester by trade -- and videos do more justice than anything I can write; however, I included a brief description below.
I created a new color set -- and proceeded to add color swatches for every 45 degrees around the Hue circle. More often than not, after adding the color swatch, one of the numbers is off by 1 digit (e.g. I entered Hue = 0, Saturation = 255, Value = 128 for Blue). After adding swatch, I clicked on a different swatch, then back to the one I created and the Saturation changed to 254. It seems to be random -- it can happen for any of the Hue, Saturation, or Value numbers.
OS: Windows 10 64bit (Version 1909 (OS Build 18363.815
Painter 2020 v220.127.116.115
NVIDIA GeForce GTX 980 Ti
AMD FX-8350 Processor