Declaring response headers as a list of Header objects
It looks like some developers are trying to generate their OAS 3 files from 3rd party tools that do not fully conform to the OAS standards. This results in inaccurate header objects. The specification states that the response headers must be:
1) A map with header name as key and Header object as value OR
2) A map with header name as key and a Reference object as value (that basically would still point to a Header object).
This implies that an array of header objects or an array of reference header objects can, therefore, not be used but the mistake is still seen quite commonly. Also, the Swagger editor itself does not seem to complain in either case.
So essentially this is invalid (at least as per the spec):