Help with debugging - stall on response size is a symptom but what is the cause?

[LetsPlay]

> nginx -V
nginx: nginx version: nginx/1.0.5
nginx: TLS SNI support enabled
nginx: configure arguments: --prefix=/etc/nginx
--conf-path=/etc/nginx/nginx.conf
--error-log-path=/var/log/nginx/error.log
--http-client-body-temp-path=/var/lib/nginx/body
--http-fastcgi-temp-path=/var/lib/nginx/fastcgi
--http-log-path=/var/log/nginx/access.log
--http-proxy-temp-path=/var/lib/nginx/proxy
--http-scgi-temp-path=/var/lib/nginx/scgi
--http-uwsgi-temp-path=/var/lib/nginx/uwsgi
--lock-path=/var/lock/nginx.lock --pid-path=/var/run/nginx.pid
--with-debug --with-http_addition_module --with-http_dav_module
--with-http_geoip_module --with-http_gzip_static_module
--with-http_image_filter_module --with-http_realip_module
--with-http_stub_status_module --with-http_ssl_module
--with-http_sub_module --with-http_xslt_module --with-ipv6
--with-sha1=/usr/include/openssl --with-md5=/usr/include/openssl
--with-mail --with-mail_ssl_module
--add-module=/build/buildd/nginx-1.0.5/debian/modules/nginx-echo
--add-module=/build/buildd/nginx-1.0.5/debian/modules/nginx-upstream-fair

Logs: http://pastebin.com/W4Tf0vcF

Here is a summary again:

Details: 
System: Ubuntu 11.10, Play 1.2.4 unzipped and installed, Nginx 1.0.5 
via apt-get 
Network: www.myApp.com points to a static IP, which is a modem/router 
with LAN address 192.168.1.1 wired to my box 192.168.1.13.  The router 
uses the NAT rule "forward port 80 to 192.168.1.13" (my box) 
Note that local access (http://localhost:9027) works fine in all cases 
Case 1: WORKS vanilla "play new myApp" works fine at
http://localhost:9027 
Case 2: FAIL vanilla "play new myApp" times out at http://www.myApp.com,

nothing received by browser 
Case 3: WORKS hacked index.html with short toy css, works via
www.myApp.com 
Case 4: FAIL Case 3 with lengthened css, long delay via www.myApp.com, 
css not used 
Case 5: WORKS Case 4 but with nginx "proxy_buffering off;", works via 
www.myApp.com 
Case 6: FAIL Case 5 with an extra css comment line, long delay via 
www.myApp.com, css not used

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,222240,222326#msg-222326