Magento 1.9.1
Porto theme

app/code/core/Mage/Checkout/Block/Onepage/Billing.php

public function isUseBillingAddressForShipping()
    {
        if (($this->getQuote()->getIsVirtual())
            || !$this->getQuote()->getShippingAddress()->getSameAsBilling()) {
            return false;
        }
        return true;
    }