Nginx, GET and POST solution for “The plain HTTP request was sent to HTTPS port”

I'm trying to create a SSL proxy for a web management console running on localhost and having no SSL support.

Here is my config:

server {
  listen                  111.222.1.1:8443 ssl;
  server_name             admin.company.com;

  ssl_certificate         tls/ssl.crt;
  ssl_certificate_key     tls/ssl.key;

  proxy_set_header        Host $http_host;
  proxy_set_header        X-Real-IP $remote_addr;
  proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
  proxy_hide_header       X-Powered-By;

  #error_page 497         https://admin.company.com:8443$request_uri;

  location / {
    proxy_pass            http://127.0.0.1:8080/;
  }
}

The proxied service is quite sophisticated and uses a lot of Post/Redirect/Get operations, network monitor shows they're all involving "http://admin.company.com:8443" and thus causing the subj.

Adding error_page 497 (commented out) solves GETs and redirects, but makes POSTs impossible. Is there any solution to this, one IP and one port configuration, which would proxy both GET and POST requests?

UPD:
The application behind proxy is a Java servlet running in the insecure mode, so I believe this is where "http" comes from, it simply takes proxied hostname and builds up URLs with "http" explicitly set.