error_log issue in php.ini

Howdy, I have found something that I find a bug in php. If I have log_errors = on in the php.ini and don't set the error_log entry, I can never set it in a php script. I have the error_log commented out in the php.ini, because I have it set in my httpd.conf file for all of my virtual hosts. But when I run php from the command line, I want to set the error_log to a file, and ini_set() always returns false, simply because error_log is commented out in the php.ini. I should be able to set this at runtime. Walt