Magento – Wrong tax calculation in paypal when discount is given

We found that gremlin during our regression on EE 1.13.0 / CE 1.8.0 and are juggling prioritization with other issues. Quick work around is to send summary info rather than line item to Paypal and it'll work like a champ.

I think the problem is that discount is calculated AFTER taxation, when paypal tries to calculate it BEFORE. I solved extending the Mage_Paypal_Model_Hostedpro_Request class and adding the hidden tax amount to the tax, resulting in

protected function _getOrderData(Mage_Sales_Model_Order $order)
    {
        $request = array(
            'subtotal'      => $this->_formatPrice($order-getBaseSubtotal()),
            'tax'           => $this->_formatPrice($order->getBaseTaxAmount() + $order->getHiddenTaxAmount()),
            'shipping'      => $this->_formatPrice($order-getBaseShippingAmount()),
            'invoice'       => $order->getIncrementId(),
            'address_override' => 'true',
            'currency_code'    => $order->getBaseCurrencyCode(),
            'buyer_email'      => $order->getCustomerEmail(),
            'discount'         => $this->_formatPrice(
                $order->getBaseGiftCardsAmount()
                + abs($order->getBaseDiscountAmount())
                + $order->getBaseCustomerBalanceAmount()
            ),
        );
...

I'm planning to put everything in an extension if someone is not able to do it. Stay in touch because I could forget about it :D

EDIT Here it is!