connection close on 500, 503, 502.

[newnovice]

I have this in config: 
---
    error_page 404 =400;
    error_page 500 502 503 504 =500 @close_conns;

        location @close_conns {
            internal;
            keepalive_timeout 0;
        }
----

I still see 502's behind returned in '$status' - Why would this happen? I
was expecting to see a 500, based on my config. 
I also see 404's - which should have been transformed to 400.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,254535,254577#msg-254577