Not sure if the title is perfect, but heres my 2cents.
I have found that vehicles explode when shot at with non explosive rounds. Sure it takes a few rounds, but the end result is that the car gets destroyed and blows up, which first of all, is rather unrealistic as it is highly unlikely, even though possible, but i guess a safe estimate is the likelyhood being 1%?
Why it is a problem. Because when getting out a vehicle when under attack, or vehicle is disabled, you may not have any decent cover nearby, so generally ducking behind the vehicle makes for good cover, and the problem is if the enemy shoots the car to zero health, it blows up and you die.