Hi, @berni. I cannot reproduce what you see when I test. I do see this site using a service worker. This means it is quite possible that the issue is a cached response on your local system.
Would you be willing to send us a HAR recording of the issue occurring? The HAR recording will tell us the source of those headers.
Also, if you delete the service worker that might fix it. If it does, that means it was a local service worker issue.
If there are other questions for us, please let us know.