Magento Coupon – Fix Discount Coupon Not Working for Minimum Subtotal

This is a bug which has been reported and was introduced in 1.9. There is flawed logic which means when using 'Stop Further Rules Processing' only the first product in the cart has the cart rule applied. Magento have said We are checking the issue as there are more reports related to it but I suspect a fix may be some time coming.

In the mean time we have created a module to fix the issue here.

In the class Mage_SalesRule_Model_Quote_Discount there is this method that adds the discount total to the list of totals:

public function fetch(Mage_Sales_Model_Quote_Address $address)
{
    $amount = $address->getDiscountAmount();

    if ($amount!=0) {
        $description = $address->getDiscountDescription();
        if (strlen($description)) {
            $title = Mage::helper('sales')->__('Discount (%s)', $description);
        } else {
            $title = Mage::helper('sales')->__('Discount');
        }
        $address->addTotal(array(
            'code'  => $this->getCode(),
            'title' => $title,
            'value' => $amount
        ));
    }
    return $this;
}

You can see here that the total is added only when the discount amount is not zero if ($amount!=0) {.
So just rewrite this class and change the method I mentioned. Remove the if statement and it should work.