Same problem here
# nginx -V
nginx version: nginx/1.2.3
configure arguments: --prefix=/usr/local/etc/nginx --with-cc-opt='-I /usr/local/include' --with-ld-opt='-L /usr/local/lib' --conf-path=/usr/local/etc/nginx/nginx.conf --sbin-path=/usr/local/sbin/nginx --pid-path=/var/run/nginx.pid --error-log-path=/var/log/nginx-error.log --user=www --group=www --with-file-aio --with-ipv6 --http-client-body-temp-path=/var/tmp/nginx/client_body_temp --http-fastcgi-temp-path=/var/tmp/nginx/fastcgi_temp --http-proxy-temp-path=/var/tmp/nginx/proxy_temp --http-scgi-temp-path=/var/tmp/nginx/scgi_temp --http-uwsgi-temp-path=/var/tmp/nginx/uwsgi_temp --http-log-path=/var/log/nginx-access.log --add-module=/usr/ports/www/nginx/work/ngx_http_gunzip_filter_module-0.4 --with-http_stub_status_module --add-module=/usr/ports/www/nginx/work/nginx_upstream_hash-0.3.1 --with-pcre
# uname -a
FreeBSD hostname 7.4-RELEASE-p9 FreeBSD 7.4-RELEASE-p9 #0: Mon Jun 11 19:47:58 UTC 2012 root@amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC amd64
2012/09/13 15:38:03 [alert] 59568#0: *4954010 zero size buf in output t:0 r:0 f:0 0000000814EE2000 0000000814EE2000-0000000814EE4000 0000000000000000 0-0 while sending to client, client: 90.133.66.18, server: hostname.ru, request: "GET /web/upload/forall/js/jquery-1.4.2_nyroModal-1.6.2_validate_capslock_jquery-ui-1.8.4.custom.min.js HTTP/1.1", upstream: "http://ip:80/web/upload/forall/js/jquery-1.4.2_nyroModal-1.6.2_validate_capslock_jquery-ui-1.8.4.custom.min.js", host: "delamour-ufa.ru"
2012/09/13 16:05:32 [alert] 59567#0: *5305581 zero size buf in output t:0 r:0 f:0 0000000800F3A000 0000000800F3A000-0000000800F3B000 0000000000000000 0-0 while sending to client, client: 92.243.167.145, server: hostname.ru, request: "GET /web/static/js/120907/jquery.admin.plugins.min.js HTTP/1.1", upstream: "http://ip2:80/web/static/js/120907/jquery.admin.plugins.min.js", host: "landlifes.hostname.ru", referrer: "http://landlifes.storeland.ru/admin/orders"