Possible bug with "proxy_intercept_errors on; " + "error_page 301 302"?

[Fabiano Furtado Pessoa Coelho]

Hi...

I have one peculiar issue with NGINX 1.22.0 + "proxy_intercept_errors
on;" + custom 302 "error_page".

Here is my simplified NGINX config:

http {
  error_page 301 302 /30x.html;
  server {
    location /30x.html {
      root /etc/nginx/custom_error_pages;
      sub_filter_once off;
      sub_filter '*HTTP_STATUS_CODE*' '$status';
      internal;
    }
    location /mysystem {
      rewrite ^(.*)$ / break; # remove "/mysystem" and only send "/" to backend
      proxy_intercept_errors on;
      proxy_pass http://php_server;
    }
  }
}

Using both "proxy_intercept_errors on;" and "error_page" directive, I
have HTTP 302 response from my php backend server (OK!), but without
HTTP new "location" header:

$ curl -v https://foo/mysystem
...
< HTTP/2 302
< date: Thu, 29 Jun 2023 17:48:31 GMT
< content-type: text/html
< strict-transport-security: max-age=63072000
...

Why? If I turn off the "proxy_intercept_errors" directive or remove
the line "error_page 301 302 /30x.html;", it works:

$ curl -v https://foo/mysystem
...
< HTTP/2 302
< date: Thu, 29 Jun 2023 18:05:42 GMT
< content-type: text/html; charset=UTF-8
< location: https://bar
< strict-transport-security: max-age=63072000
...

Is this normal? Why can't I have a 302 custom error page using
"proxy_intercept_errors on;"?

Thanks in advance.