If it works in a single mission it should work in a campaign generally.
I also had that opinion but apparently it isn't that linear as I'm experiencing with this issue.
In the campaign on the weapons selection screen does it only let you choose a single bomb on each pylon? Is the bomb type exactly the same as the one you use in single missions?
Yes and yes. I even opened the campaign files where the initial weapons available to the squadrons is defined and the aircraft's loadout.ini file and it seems that the weapons are the same.
I'll post a couple of screenshots below to show you what I'm experiencing:
Here is the loadout screen in a single mission:
And as you can see, you can for example (just like the real aircraft) either load a total of four (4) 1000lb bombs on the inboard pylons (2 on each pylon) or alternatively you can load a total of two (2) 1000lb bombs on the inboard pylons (1 on each pylon).
Next, is the loadout screen with the same aircraft but in a campaign mission:
And here as you can see, you can only load a total of two (2) 1000lb bombs on the inboard pylons (1 on each pylon).
On the inboard pylons it likely uses RackType=2br_uk_jag on the inboard pylons - is that whats in your loadout.ini?
Yes, I can confirm that's what I have on the aircraft's (Jaguar) loadout.ini file. Here's the my Jaguar GR1 loadout.ini file, you can download it and check for yourself:
https://drive.google.com/file/d/0BwK-B4mRQeNLUVY1MXRRRXV0Ukk/view?usp=sharing