Log module

hello:
when i using the log module to write the acess_log.there are three
set-cookie line in reponse hearders, But the log module only writes
the first set-cookie of response headers into log.
here is 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” $upstream_addr ’
‘$http_cookie $request_time set_cookie=$sent_http_set_cookie’;