Thanks for troubleshooting, Lynx3d.
I checked advanced color selector in float and docked mode and there is no differences.
Also I tested WindowsInk in other software. Similar issue with color picker also have ClipStudioPaint and Rebelle. Photoshop 2019 is OK, but I remember visually similar glitches in previous versions since they switched plugins from flash to html engine. Paint Tool SAI is OK too. In PaintstormStudio I didn’t find switcher windowsink/wintab but tested with option in wacom driver settings and it is OK.
And, just in case, I checked it with Intuos5 (main tablet is Cintiq13hd) and as suspected there is no differences.