If you hold down left mouse button with the SMG and empty all of the ammo (it seems to work even with very low amounts of ammo left) even after the ammo has depleted it will continue to show the visuals of the gun firing (animation of gun kickback, the flash at the end of the barrel and lighting) also, the sounds will continue to play; as long as you keep holding down the left mouse button. No projectiles are actually fired so it is not really a serious bug.