Is there a length limitation on file extensions?

[j.o.l]

yes, nginx -t reports OK.
I tried the empty types block with default_type as suggested - no change to
the behavior. 
I verified that there is no other block processing the request. There is no
other block that uses that certificate on port 443, and the port 8080 is
used for that server block only. I also added an access_log to that server
block redirecting output to a different file, and yes, the output goes to
that different file. I even defined my own log_format that logs
$sent_http_content_type, and it reports application/x-ms-application for
http, and - when using https...
Any other idea what to try or check?
Thanks a lot!

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,265148,265197#msg-265197