Non penetrating hit

[Aeraaa]

Usually when a vehicle is hit by a projectile it is either penetrated (with some minor damage or completely destroyed) or the round has no effect on target. However some times I see the message "Non-penetrating hit" in which no damage is being caused to the vehicle hit plus it also has the fast ricocheting sound you hear when a vehicle takes non catastrophic damage. Anyone knows what is supposed to have happened in this situation?