OK, so... I'm trying to have the "shipping=billing" UNchecked by default so the customer gets to see both billing AND shipping address at the same time when going through Guest Checkout.

I've changed includes/classes/OnePageCheckout.php on line 169 from
Code:
public function getShippingBilling()
    {
        $_SESSION['shipping_billing'] = (isset($_SESSION['shipping_billing'])) ? $_SESSION['shipping_billing'] : true;
        return $_SESSION['shipping_billing'];
    }
to
Code:
public function getShippingBilling()
    {
        // BOF shipping=billing default to false
        $_SESSION['shipping_billing'] = (isset($_SESSION['shipping_billing'])) ? $_SESSION['shipping_billing'] : false;
        // EOF shipping=billing default to false
        return $_SESSION['shipping_billing'];
    }
When a customer starts checkout, both billing and shipping address fields are visible and if you fill out billing address, save it, fill out shipping address and save it, everything works fine and you can continue through checkout.
BUT, if you fill out billing details, save it and then tick the "shipping=billing" checkbox, the shipping address gets populated and properly assigned, but there's still no payment/shipping options available. Editing ANY of the details (email, billing OR shipping) and saving it bring up the shipping/payment section and allows to proceed.

What am I missing? Is this controlled anywhere else that I'm not seeing it? Thanks in advance!