Hmmn, just read the manual again. Page 220 ...
"... due to limitations of the targeting computer, it is not
possible to mix Super 530D missiles with air-to-ground weapons, and not possible
either to mix different kinds of air-to-ground weapons. "
So, as per the picture on page 225, if rockets are fitted, then only a fuel tank on the centre pylon is possible.
This is a Mission Editor payload editor configuration issue.
Still, some bugs in the PCA, though :(