I'm not sure if is a mechanics or a text bug but when you have 6 mercenaries and try to hire a 7th you get this message :
"You don't have enough Mercenary Captain skills!" regardless of what you Mercenary Captain skill is.
Not a game breaking bug but I'd rather change the text to :
"You have enough mercenaries buddy. Maybe you should try easier fights ? Or suck less ? I don't know, I'm just saying..."
or something more appropriate