Its pretty random but it has happened quite a few times with the mohawk, strider, hunter, pickups and crossovers
Videos:
https://www.youtube.com/watch?v=3RVUhzgeX50&feature=youtu.be&t=1m11s
https://www.youtube.com/watch?v=5dAqK2iLUKg#t=23
In both cases both vehicles were full health and it only happens if you kill the driver.