Bizarre? Logging: $variable_* vs $upstream_http_*

[icqheretic]

Consider this configuration fragment:


log_format  test_log 'TEST: [$origin_ip] [$upstream_http_content_type]';

location / {
    access_log      /tmp/test.log test_log;
    set $origin_ip $upstream_http_content_type;

    proxy_pass             http://127.0.0.1:6060;
}



Why am I seeing this in the log file "test.log"?

TEST: [] 

Why is set not being loaded with $upstream_http_content_type? Shouldn't I see:

TEST:  

Any ideas?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,26404,26404#msg-26404