MSP_CashonDelivery_Model_Order_Total collects bug

Total.php

<?php
/**
 * IDEALIAGroup srl
 *
 * NOTICE OF LICENSE
 *
 * This source file is subject to the Open Software License (OSL 3.0)
 * that is bundled with this package in the file LICENSE.txt.
 * It is also available through the world-wide-web at this URL:
 * http://opensource.org/licenses/osl-3.0.php
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to [email protected] so we can send you a copy immediately.
 *
 * @category   MSP
 * @package    MSP_CashOnDelivery
 * @copyright  Copyright (c) 2014 IDEALIAGroup srl (http://www.idealiagroup.com)
 * @license    http://opensource.org/licenses/osl-3.0.php  Open Software License (OSL 3.0)
 */

class MSP_CashOnDelivery_Model_Order_Total extends Mage_Sales_Model_Order_Invoice_Total_Abstract
{
	public function collect(Mage_Sales_Model_Order_Invoice $invoice)
	{
		$order = $invoice->getOrder();
        $payment = $order->getPayment();
        $method = $payment->getMethodInstance()->getCode();
        if( $method == 'msp_cashondelivery' ) {
            
            $amount = $order->getMspCashondelivery();
            $baseAmount = $order->getMspBaseCashondelivery();
    
            $invoice->setGrandTotal($invoice->getGrandTotal() + $amount);
            $invoice->setBaseGrandTotal($invoice->getBaseGrandTotal() + $baseAmount);
        }

		return $this;
	}
}