The at-5 and 9m14p missiles will veer off target when you are inside the vehicle and use the command fire to get your gunner to fire the missile.
They appear to work fine when you are outside the veh and the veh is manned by AI and this only seems to occur when the player is inside the veh with the AI as his gunner and you give the Ctrl left mouse button command fire.
They player himself can fire and guide the missile just fine if he is the gunner with AI in the veh.