I managed to make a ghost person. The way it happened was that I went to equip an empty character slot, and then when I exited there was the third spot unlocked.
Nice find, I bet this has existed since the first version without anyone discovering (or at least reporting) it. Seems like when you go to equip menu without a character in that slot, the game will generate a new one but it will have a zero grid size. And because they have no grid (and that isn't supposed to even happen) they are scaled way down and seem almost invisible.
Luckily that doesn't completely break the game. You just get a free flea sized party member who can't equip anything.
I found it on accident was curious what would happen if i did it does have some minor problems of if you try to put something on that guy the item takes up the whole screen of the menu there but that's really it for issues I saw I say it should be kept and used as an easter egg for those of us who know