id,summary,reporter,owner,description,type,status,priority,milestone,component,version,severity,resolution,keywords,cc
10595,Allow plugins to add columns to user management screen,martinv5,,"It's here on line '''1974''' in wp-admin/includes/template.php:

apply_filters('manage_users_custom_column', '', $column_name, $user_object->ID);

An '''empty argument''' it passed to the filter instead of the actual column name.

See the file here http://core.trac.wordpress.org/browser/branches/2.8/wp-admin/includes/template.php 

Or am I missing something?

Thanks,
M.",feature request,closed,high,,Administration,2.8.3,trivial,duplicate,manage_users_custom_column user management,