Magento – Why does a free shipping promotion make all shipping options free

So here is how I did it.

First, I have used more appropriate event for that purpose, that is sales_quote_collect_totals_before. And second, I needed to comment out (in local copy of course), one line in Mage_SalesRule_Model_Quote_Freeshipping:

public function collect(Mage_Sales_Model_Quote_Address $address)
{
    parent::collect($address);
    $quote = $address->getQuote();
    $store = Mage::app()->getStore($quote->getStoreId());

    //$address->setFreeShipping(0); # clime: we set this in module
    ...
 }

That is it. The following now works well:

$address = $quote->getShippingAddress();
$address->setFreeShipping(true); # the value must be true, not 1

It works well in single shipping mode. Multishipping is probably going to need some adjustments.

There is the same bug on Magento 1.6. This fix is working and I hope to work on Magento 1.7 too.

Open app/code/core/Mage/SalesRule/Model/Validator.php and add below this:

protected $_baseRoundingDeltas = array();

this code:

protected $_address = null;

also in protected function _getAddress below this:

if ($item instanceof Mage_Sales_Model_Quote_Address_Item) {
    $address = $item->getAddress();

add this:

} elseif ($this->_address) {
    $address = $this->_address;

and finally in public function reset above this:

return $this;

add this:

$this->_address = $address;