Request Validator is no longer created when requiring headers?

2/3 months ago we deployed a lambda and API Gateway with serverless - in the config we had the following to require a specific header:

          method: POST
          path: new_path
          integration: lambda
              a-required-header: true
              application/json: ${file(./a_request_schema.json)}

We noticed recently that this header is no longer required and we can POST to the endpoint without the header populated.

I noticed in the docs, headers seems to be within parameters - have tried this also, but with no luck.

Is this a known issue or are we doing something wrong?

Is there certain scenarios in which required headers/request validators work/don’t work?

Think you are seeing the same kind of stuff i have posted about here How do you add a request validator to api gateway?

since i want to drop the plugins and go native if possible