I am playing the original Playstation version of FFT and I realized that during the second encounter at Dorter (in ch2 with agrius etc.) I realized the leader, unlike most characters with unique portraits, could actually be invited. I managed to invite him and then something weird happened. After the battle, instead of adding him to my party, he somehow took the place of and erased my other thief (losing his unique portrait along the way). Has anyone else heard of something like this happening? Sorry if this is posted in the wrong place or if this is an old topic but i couldn't find info on this anywhere.

are you sure your original thief just didn't steal all his stuff?

Congratulations, you found another bug. Quite a few of those floating around.

"are you sure your original thief just didn't steal all his stuff?"

and put it on and lose his abilities and gain 4 levels? I'm pretty sure. I'm going to try it again later to see if i can get similar results.