Get Ms. Mowz before going to Keelhaul Key. Swap her out for another partner, then open your item inventory. Try to use an item on a character, and you'll see Bobbery in the list replacing Ms. Mowz! (At this point in the game, Bobbery is next to join your party.) Using an item on "Bobbery" causes his name to flash on the list, but any HP-recovering item will be wasted because Ms. Mowz will not get it. If Ms. Mowz is your current partner, the list is normal.