This is related only to the /etc/init.d/php5-fpm file.
On reload command the script send a SIGHUP instead of SIGUSR2 as documented in php-fmp. The current behavior kills the master process. This has been corrected in latest releases of php-fpm for debian sid and unstable as stated here http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=645934
It would be nice to have it corrected in dotdeb packages too.