I have my FCGI server send "HTTP/1.1 505 Version Not Supported\r\nStatus: 505 Version Not Supported\r\n\r\n".
In nginx.conf, I have:

fastcgi_intercept_errors on;
error_page 505 /errpage;
location /errpage {
try_files /version_not_supported.html =505;
}

If version_not_supported.html is not found, I expected nginx to display "505 HTTP Version Not Supported" on the browser page, and to return "Status Code: 505 HTTP Version Not Supported" in the HTTP response. Instead, I got a blank page, and the HTTP response shows a Status code of "505 OK".

Note NGINX displays the correct error message and Status code for other error codes such as 400, 401, 403, 404, 500, etc. Just for 505, NGINX would not return the proper error message.