When you convert someone to another role, whether its Mason, Cult or Yakuza (haven't really tried out Zombie much but its easy to assume this happens as well) there are several glitches related to other roles (mostly 3rd parties)

Here is the list, at least the ones i can think of, and im not sure if it happens 100% of the time, but it does happen more often than not

Thulu: If you convert someone that has gone insane due to visiting the thulu, they will be able to speak again. This may be intentional for Mason and Cult, but it shouldn't happen for Yakuza, and im pretty sure it does.

Cupid: If one of the people they set up to be in love gets converted, Cupid will not win even if the lovered people are alive at the end of the game. Neither will one die if the other does.

Mistletoe: Same as cupid, if a peson picked to be in love gets converted, it will not count anymore.

Alien: Same as Cupid and Mistletoe, if a probed person gets converted, they wont count as probed anymore.

Poisoner: If the person poisoned gets converted, they will be saved from poison and will not die.

Arsonist: If they douse someone and they get converted, they will not die when the arsonist fires up.

These are all i can think of right now but there may be more.