yeah, it should work in polyphonic patches.
the comment means, one instance of that object is monophonic, i.e. one note at a time, so you need to put it in a poly sub patch to get polyphony.
the issue we have is modulation sources don't work in polyphonic subpatches, and keyb mod happens to be an example of that....
personally I don't use modulation sources, (I prefer explicit wires) hence why I instantly replaced it... and then promptly forgot Id replaced it.... and blamed the phasor