It's not a bug it's how the system is designed. If you go onto a caster class all skills you don't have mp for are greyed. This works on the same principle, flawless synth is a skill that can be used on its own without makers mark that's why it becomes unavailable if you don't have min cp. If it was programmed to be a makers only skill then it would be greyed unless makers was active. I say it should stay that way to force ppl to use it right