Php auto_prepend_file

I am running PHP under PHP 5 FastCGI, and I am trying to set up a site to use php’s auto_prepend_file function. I have the directive set in the .htaccess file, but it never seems to hit. Here is the line in the htaccess:

php_value auto_prepend_file debug.php

and the contents of the script is:

<?php $fh = fopen('debug.txt'); fwrite($fh,'debug'); fclose($fh); ?>

The script logs debug correctly when called directly, but not when supposedly included using auto_prepend_file.

Can anyone tell me what I’m doing wrong?[hr]
Nevermind, I went through a custom PHP.ini and it’s working now.

For the record: php_value only works under mod_php. It doesn’t affect PHP running as FastCGI.