I'm getting sick and tired of dropping a crap ton of money into car customization only to have the damn thing disappear after a cutscene.
Me too!!! Though, most of them if you park far enough away, they will still be there.
I also found out, if you mod the character's default vehicles, those changes are permanate to the vehicle even if you lose it. So when you go back to the safe house, the new vehicles are changed as well.