Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 11834)
+++ wp-includes/user.php	(working copy)
@@ -394,7 +394,7 @@
 		$meta_value = stripslashes($meta_value);
 	$meta_value = maybe_serialize($meta_value);
 
-	if (empty($meta_value)) {
+	if ('' == $meta_value) {
 		return delete_usermeta($user_id, $meta_key);
 	}