proxy_cache 404 doesn't add headers

[mankins]

Hi.

In nginx 1.0.2 on Fedora, I'm using the proxy_cache in conjunction with
add_header to add the following header with cache-status (MISS,EXPIRED,
etc.) after the cache check:

add_header   X-Cache
"$upstream_cache_status,$upstream_status,$upstream_addr";

This works as expected for http status codes 200, 301, 302, but fails to
work for 404.

I've verified that the cache is actually working for 404 requests
(upstream sees no requests), but the extra add_header fails to get
added.

Any insight onto this behavior would be great. 

Thank you,
Matt Mankins

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,199145,199145#msg-199145