I have problem somewhere between nginx and php-fpm. When I use keep-alive connection for fastgcgi php-fpm, there is often problem with loading page. Page not completely loaded. I tried to debug using wireshark, and see that php-fpm send to nginx coplete reply, but nginx to client sent incoplete page. Size of incomplete page is defined by chunk size. For test, download http://kinohled.cz/bugreport.tar.gz and run ./showBug.sh . You will se:

Run Nginx on port 9876
Run php-fpm on port 6789
Correct size of answer is 16172;
keepalive on, size: 8002
keepalive off, size: 16172
Next test (1 of 5)-
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Tested on Debian Squeeze and many version of Nginx/PHP-FPM . Error shows on default Nginx/PHP-FPM version by Debian Squeeze by dotdeb.org .

nginx/1.2.6
PHP 5.3.21-1~dotdeb.0

On Nginx error log:

upstream sent unsupported FastCGI protocol version: 0 while reading upstream

Any suggestion ?