Don't know if anyone else has had this happen , but if I build a constructor set it to upgrade then while its upgrading build a starbase with it . It will become a starbase and still upgrade to another ship . Then if I upgrade it back to constructor , and try to construct a starbase it acts like it's a starbase . If I add anything to it, it will disappear and about five turns later crash the game . Probably just one of those things to avoid doing . I just thought it was strange it doesn't cancel the upgrade.