PHP-FPM not writing to error log

I'm running PHP-FPM 5.3.10 with Suhosin Patch 0.9.10 and Nginx 1.2.0 on Ubuntu 12.04

I've configured error logging for php in /etc/php/fpm/pool.d/mysite.conf as:

php_admin_value[error_log] = fpm-php.mysite.log
php_admin_flag[log_errors] = on

but this file isn't created and if I create it manually it doesn't get errors logged.

I read about a bug here: https://bugs.php.net/bug.php?id=61045 I'm not sure if this is the same thing and I'm not sure how to upgrade because I installed with aptitude install php5-fpm and that package doesn't seem to have been upgraded.

Any suggestions?