I posted this into bug tracking system two times already but it disappeared (was it deleted??)
There's a bug 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.
Can we get this repaired? Or is there something I'm missing? I use manage_users_columns to add new columns, but I need this manage_users_custom_column to be able to output HTML into that column.