To this day, I don't know why this restriction even exists in the first place, so if someone has an answer, I'd appreciate it. Is it something related to the game's code? All this does is complicate things and force players to jump through hoops to avoid this unnecessary restriction. I mean, your retainer can't even have a map in their inventory and sell one at the same time, which is such an inconvenience. When doing maps, people usually wanna farm them, so they need more than 1 (or 3, if you count the saddle and an already deciphered map) on their character.