Shouldn't the skill go up to lv30?

I was in my kanna, leving a skill, then i wanted to make a skill to level 30, but i couldn't, the skill showed lv21 but i couldn't with the mastery book lv30, and doesn't seens to even have a book 30 for that skill in GMS, why?:f6:

It has a 21 because you're using Combat Orders. It maxes it 20.

I think you are right, sorry , so the skill max lv is 20 then?

That skill doesn't even go to level 21, its 20 (+1) so either you left it at level 19 and CO is bringing it up to 20, or the skill is maxed out to 20 and it goes no higher even with CO.