Heavy Warheads upgrade for helicopter got nerfed or this is a bug ?

So in the old version of the game, when i added the Heavy Warheads upgrade to the helicopter, i would get 12 aim guided rockets. But after the recent update, some times i am getting the 12 rockets, but sometimes i only get 7 rockets. Maybe it is happening only in some maps like Liberation Peak but i'm not sure. So is this a bug ?