So I've come across a bug in Heroes 2 Gold (i'm playing the expansion right now). I can't see it mentioned anywhere else (maybe i just haven't looked thoroughly).

1) If i build a ship, i can't build anything else afterwards.
2) If i build something, i'm allowed to build a ship afterwards.

I feel like if i do #2, i'm cheating. I feel like that's the bug. But it COULD be the #1 instead, i dunno.
Any viewpoints/clues?

Hmm... I guess it was present in patches changelogs. Ofc i can miss which one game patches mentioned it since many titles we have and a lot of years pass.
What you say looks like a bug. And workarounds to get off of it is deffinetly not cheating/abusing.

GOG didnt make proper releases for DOS games. They use DOS version as main even if originally it was opposite WIN version was main and most updated-fixed. Most updates is WIN Gold of this game and initial version main are Heroes2_w. X-com 1/2 (second silently have patched win version even with last fix made by 2K as xcom2_patched.exe) are bugged here cause only Win version get most bugs fixes last updates. And that for all games here. All of them get ripped from win exe (just why nlt keep them as alternate?). Heroes 2 for some(none) reson split to separate win build.

ScummVM all releases here are entirely repacked versions not possible to use without ScummVM.

And subj game originally DOS+WIN at GOG was split to two differ builds. Win version available as separate installer in goodies section. This one alternate* version actually main and most bug-fixed.
(polish localisation also use windows build but DEU and FRA based on DosBox build).

For some games GOG use highly outdated game+addon builds as source for their DosBox build instead of latest "Gold edition" that originally come as Win-executable only. Reason of making DosBox/ScummVM emulated(/modded for ScummVM as this one are highly modded engine not an emulator) - GOG Galaxy and make "easier to use" releases for it. Although DosBox/ScummVM actually require tweaking configuration files finding proper values for your PC.

So try to look did Win version have that bug(s). Probably you need restart mission for test it.

The original Macintosh version of HOMMII has the same issue. I don't know if they fixed it in the Windows version.

The game has worked this way since Day One. Whether it's a bug or not, it's just the way the game is and has always been.

So don't build a ship till you're done building other things. :)