In Krita, we can have floating point spaces. For these spaces, KoColorSpaceMaths knows that the unitvalue is 1.0, which is important for all sorts of maths.
However, for Lab and CMYK, the unit value isn't 1. For lab it's 0-100, -128-127, -128-127 and CMYK is a complete mess in this case.
This means that all KoColorSpaceMaths operations for these are broken. Including fromNormalisedChannels(which I use for the selector) and KoColor::fromXML(needed for KPL).
There was a similar issue for the specific colorselector, which ademko fixed back then by making Krita ask LCMS what the maximum and minimum values for a certain value are. However, these are stored in KoColorChannel, which doesn't seem to live close to KoColorSpaceMaths at all.
I do NOT know how to fix this. I lack the technical knowledge.