I have certain ex-NPCs who have some weird behaviours when the go visiting on another lot. They walk into the house as if they own it and stay until like 4 o'clock in the morning...sometimes even longer.
I had the same experience with the ex-NPCs. Uninvited ex-bartenders barging into the house everyday (it has nothing to do with their personality), constantly primping ex-Divas/ex-Mr.Bigs, constantly farting ex-Slobs, borked community outfits of ex-Uni NPCs and so on. I was so sick of them that I Delete 2'ed many ex-NPCs, until I found out
how to strip NPC code from the character files. Now I can hang onto the good-looking ex-NPCs for breeding purpose.