Hey,
First of all, I'm sorry if this was done on purpose, since I've checked out if the problem was recurring while using a car - not to say all.
Still exploring the visual-vehicles/structures; I've noticed a weird behavior, which isn't as important as my previous report.
When you're driving a quad, you can open a door if you're in front of it, without the need to disembark from the quad.
Update: Bigger doors are also openable from a vehicle.