Yes this is a dayz "feature" called "flying car bingo"
no but really....its part of the base game engine, and we use no vehicle damage mod so that you dont destroy your car every little time you bump into something while driving....which makes it worse unfortunately.
LOL I have lost so many cars
I think the trader sold cars are the most likely to disappear.
I haven't been able to get more than one of those to save ever but it's the same on every server that uses that mod.