I'm fairly sure this is a bug and not a feature.
When I get an airstrike and full heal/reload from a killstreak, the smg sometimes gets stuck on 27 bullets and will no longer fire; only giving the familiar click of an empty gun.
Currently, switching to the spade and left clicking, then switching back to the smg, firing one bullet, then reloading fixes this for me. I was wondering if anyone else had this problem?