Thank god for this thread. I have also hit this situation, although I'm not sure mine is a bug. Previously while still at the 'do 3 jobs...' stage of the campaign, I got so frustrated at not being able to complete said 3 jobs, I went out looking for every Xiati I could find to try and develop a technique to fight them. In doing this I found the Xiati Starbase in Xiltro and practiced on it - until it died
and then I did the same to the one next to their Homeworld.
So I hope that Starbase isn't a target later on
Thanks again for a solution.