When I got the ability to build huge ships, I created a new design with 10 constructor modules, and a slew of sensors and drive modules. Basically a very fast deployment capability.
However, when I click on construct starbase, nothing happens. I tried "upgrading" this to a design with only 9 modules (thinking there might be an issue with double digits) but that didn't solve the issue either. This ship IS capable of building a shipyard (completely consumes the ship) but that's not what I wanted to do. I wanted to build a really souped up starbase in one go.
Please investigate this bug at your earliest convenience.