Index: wp-admin/includes/class-wp-users-list-table.php
===================================================================
--- wp-admin/includes/class-wp-users-list-table.php	(revision 21284)
+++ wp-admin/includes/class-wp-users-list-table.php	(working copy)
@@ -53,7 +53,7 @@
 		);
 
 		if ( '' !== $args['search'] )
-			$args['search'] = '*' . $args['search'] . '*';
+			$args['search'] = '*' . trim( $args['search'] ) . '*';
 
 		if ( $this->is_site_users )
 			$args['blog_id'] = $this->site_id;