> I reported the issue to my reseller and the response was essentially "yeah, you're gonna have to take that into account."

> I guess it's not really a bug per se, just hidden behaviour that you have to learn about and take into consideration.

I'm not that kind of engineer, so I may be missing something, but it sounds like the reseller snowed you into blaming yourself for their faulty software.

I get what others have said, that a structural engineer is responsible for the things they produce and for doing whatever is necessary to verify correctness, but that doesn't mean that software engineers get to pass off responsibility for the things they produce.