Upstream_cache_status -> Return ' - '

Hi, I have 2 version of Nginx running ; 1.2.1 and 1.4.1. Basically 1.4.1 is just newly installed and copy all configuration files over.
It works perfectly fine. Just one thing I notice that the upstream_cache_status doesn't give response like "HIT", "MISS" but rather "-".
I have my variable configured under HTTP which work for 1.2.1. Any idea?

##### My log format #######
log_format main '$remote_addr - $remote_user [$time_local] "$request" '
'$status $body_bytes_sent "$http_referer" '
'"$http_user_agent" "$http_x_forwarded_for" '
'## $upstream_cache_status ## '
'Cache-Control:$upstream_http_cache_control , '
'Expires: $upstream_http_expires';
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