I believe it happens because there are some spatial shortcuts taken with physics collision checks which make large vehicles have greater chance of being in one world block but having their front bumper intersecting with a static obstacle in another world block at the same time, allowing the vehicle to go partially inside the obstacle for quite a bit, until the vehicle moves enough to change its logical world block (detected only from its center point) and the collision becomes properly detected, thus getting a huge collision response for having penetrated the obstacle so far.
Obviously this is by far not robust enough for the action RWR has these day, while it might have been enough when vehicles didn't exist. It just still works well or usable enough so that I haven't considered it something to intervene with. Would help if maps would avoid placing objects near world block boundaries, but this will become fixed eventually anyway.
For now, let's just enjoy the ride
