1st slot shipyard, nothing else built it works. (70% discount)
2nd slot as stargate it breaks. If stargate is demolished it works again.
2nd slot as station it breaks. If station is demolished it works again.
2nd slot shipyard, shipyard in slot 1 it works. (70% discount, working as intended, only 1 bonus supposed to be given)
2nd slot shipyard, stargate in slot 1 it works. (70% discount)
2nd slot shipyard, station in slot 1 it works. (70% discount)
Any orbital going into slot 3 while there is a shipyard in 2 breaks discount. Demolishing the orbital restores it.
3rd slot shipyard ALWAYS provides 70% discount even if the orbitals in the lower slots are shuffled.

The bug is fairly straightforward. Any structure built after the shipyard breaks the discount.

Its slot position, not time built. A slot 3 (unlocked by stargates) shipyard always works, and once its there, any changes or removals of slot 1 or 2 doesn't effect it. Just need to build the stargate in slot 1 or 2.