manage_users_custom_column not firing?

In working on some improvements to a plugin, I wanted to add a column to the users admin screen. I have already added a column to the posts management screen with no difficulty, but following the same procedure with users seems not to work. The code I’m working with:

add_action('manage_users_custom_column', array(&$this, 'do_users_custom_column'), 5, 2);
			add_filter('manage_users_columns', array(&$this, 'add_users_column'), 5, 2);

The extra column is being added, but the do_users_custom_column action is never firing. Is there something odd with this particular action, or is this a bug? I didn’t find anything in Trac on it.