well ... I was in singleplayer, and spawned several crown vics, and turned on all their police lights to admire them... and after a minute, one of them flipped upside down and teleported to where I was standing. then another one followed suit. I wasn't colliding with them, they were just shaking upside down. I went to their actual location and bumped them, and they went back to normal.
...then one of the others started rapidly steering back and forth, then flashing its hidden nodes, and then did the same thing as the others.
so....
I might have broken something. or the crown vic is now haunted.
but i'm honestly not sure how I could have broken it, and really, the best way for me to see if this is actually a problem, and get ideas on how to fix it, is to let other people use it. so i'm going ahead as planned. but right now, I need sleep.