I have found that you can have wing smoke on pylon 1 & 9 with the central fuel tank selected perfectly fine. However if you try placing a smoke on pylon 5 in the centre then the wing fuel tanks won't be placed on the aircraft. I tried placing the wing tanks on first and then placing a smoke on centre after, this just results in them removing the fuel tanks after placing the smoke on. It would appear that there are some issues when it comes to certain load outs.