Basically just what the title says.  During a skirmish vs the AI I built a starbase in a system that the AI was assaulting.  The second I clicked the deploy button on the cruiser the starbase opened fire, even though it was still under construction.

Observations:

-Build graphic looks normal

-Build status bars were behaving normally

-Hitpoints were gradually building up, just like they should during a build phase

-The starbase fired its plasma guns on a nearby enemy frigate, causing damage

-I was able to give attack orders on various other enemy ships while the starbase was still under construction

Edit: Oops, forgot to add that I'm using the recent build 0.91.002.