Forgive me if this has already been reported. My search didn't turn anything up, so I'm assuming it hasn't.

I believe there is an issue with the Terran economy stations. I've noticed that they details screen indicates that there is another possible module upgrade (i.e. 6/7 is indicated), but when you send a constructor the game reports that there are no more upgrades available. I can't be 100% sure, but I believe the Smart Droids module is the culprit.