Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 21689)
+++ wp-includes/user.php	(working copy)
@@ -372,6 +372,7 @@
 			$this->query_vars = wp_parse_args( $query, array(
 				'blog_id' => $GLOBALS['blog_id'],
 				'role' => '',
+				'post-type' => '',
 				'meta_key' => '',
 				'meta_value' => '',
 				'meta_compare' => '',
@@ -432,7 +433,7 @@
 			$orderby = 'display_name';
 		} elseif ( 'post_count' == $qv['orderby'] ) {
 			// todo: avoid the JOIN
-			$where = get_posts_by_author_sql('post');
+			$where = get_posts_by_author_sql($qv['post-type']);
 			$this->query_from .= " LEFT OUTER JOIN (
 				SELECT post_author, COUNT(*) as post_count
 				FROM $wpdb->posts