I've yet to see this happen or be reported. I was playing a custom race using the Arcean tech tree. No AI was in the game that used that tree. Anyway, the planet on which I was building the Stellar Forge was conquered by the AI. I promptly recaptured it but found that the Stellar Forge was no longer being built. No problem I thought. That fact just indicates the AI could not build it because it did not have the requisite tech. However, when I pulled up the production list to start building the Stellar Forge again, it was no longer available on any list (New, Old, All). I tried a different planet and could not build it there either. The option of building the Stellar Forge was lost. I don't believe this is working as intended.