I've had sims that aren't meant to be there suddenly appear without warning pee themselves, and pass out.
Hoped in vain it would be a bug, but seems to be one of Maxis queer jokes.
I delete them.
Why? Well, if that is so - if itīs not a bug but strange humor (JM most probably loves it) - Iīll use this sim and further ones to populate my community graveyard. No more dirty hands from killing CAS sims designated to be ghosts - keeps my character files clean.