When I select any of my other characters, the 3rd weapon slot appears with whatever Kana has equipped in that slot. If I click on the slot, Kana changes to it (even if I had a different character selected).
Not a big deal as it doesn't actually help or hurt me in any way - but it is a strange display/UI bug, and I'm not sure what would happen if I had another Amuaua with a 3rd weapon slot in the party.