There was a post a while ago about a user receiving rocket like projectiles when triggering VB-IED's. I have managed to create what he was referring to by shooting the IED's that are attached to vehicles and suicide bombers. By shooting the C4 attached to the bottom of a car it shot out and hit a nearby hill and exploded. I also managed to find the same thing by shooting the C4 on a suicide bomber. This does not seem to occur every single time but frequently enough for it to be noticeable if you are trying to reproduce it.
Video: http://www.twitch.tv/spyderblack723/b/637802454?t=20s
if you skip to 20 seconds in, you can see that when I shoot the IED under the car, it shoots out and hits the ground nearby. Sometimes it is much more noticeable though and flies off to a nearby hill taking a few seconds before the explosion goes off.
The same thing happens again here and is slightly more noticeable - http://www.twitch.tv/spyderblack723/b/637802454?t=3m09s
Maybe this line of code in the createVBIED is the issue - "M_Mo_120mm_AT" createVehicle getposATL (_this select 0);
Is it possible that this creates a rocket that shoots out the side from time to time? Just a super random guess.
Testing was done with only CBA and ALiVE.