Answer
This has been traced to a bug on Postman's own side (there's an open GitHub issue against Postman for this exact symptom), not an issue with the IFS API's own OpenAPI specification — trying the OpenAPI v2 and v2-minimal spec variants for the same API doesn't avoid it either, since the underlying issue is in how Postman parses certain specs, not which spec version is used. If you hit this on a specific API, it's worth checking Postman's own known-issues tracker before assuming the API export itself is broken.