Challenge: Engineer 3 - Vehicle Destroy Bug

Challenge Engineer 3 - “Deal damage to aircraft with launchers as Engineer.” does not seem to register progress for damage when the aircraft is destroyed, at least with RPG.
Ex: Shooting down Attack Helicopter with 1 RPG does not progress challenge. 
whereas: Hitting full health Blackhawk with 1 RPG, that does not destroy the heli, progresses achievement.