Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 16407)
+++ wp-includes/user.php	(working copy)
@@ -59,7 +59,11 @@
 	}
 
 	wp_set_auth_cookie($user->ID, $credentials['remember'], $secure_cookie);
-	do_action('wp_login', $credentials['user_login']);
+	if ( is_a ($user, 'WP_User') ) {
+		do_action('wp_login', $user->user_login);
+	} else {
+		do_action('wp_login', $credentials['user_login']);
+	}
 	return $user;
 }