Paypal not finding ship to address

Store URL: http://www.galleybeggar.co.uk/book-store/
WordPress version: 3.8
WP e-Commerce version: 3.8.13.1
Gold Cart version: N/A
Theme: Custom

I did this:
Tick the ‘shipping address is same as billing address’ box.

I expected WP e-Commerce to do this:
Send the shipping address details to Paypal.

Instead it did this:
Caused Paypal to give this error:

Unable to process payment. Please contact the merchant as the postal address provided by the merchant is invalid, and the merchant has requested that your order must be delivered to that address.

Further details:
The error occured after upgrading WP to 3.8 and WP e-Commerce to 3.8.13.1. The message only appeared when the above-mentioned box was ticked – people could still buy items by manually entering a shipping address.

The error doesn’t appear when I comment out lines 145 to 148 in /wp-content/plugins/wp-e-commerce/wpsc-merchants/paypal-standard.merchant.php, like so:

if ( (bool) get_option( 'paypal_ship' ) && ! $buy_now ) {
  //  $paypal_vars += array(
  //    'address_override' => '1',
  //    'no_shipping' => '0',
  //  );

Everything is working now but I’m hoping someone is able to explain what triggers the error and to provide a better solution. I’m not sure what exactly the ‘address_override’ and ‘no_shipping’ variables do when set to 1 and 0, respectively.

I should mention that, after the upgrades, I also installed the ‘Members Only: Membership & Subscription plugin for WP e-Commerce’ plugin (version 2.9). The site’s error log showed the following entry at the time the error appeared:

galleybeggar.co.uk [Mon Dec 30 11:35:13 2013] [crit] [client 22.211.115:41124] AH00529: /home/sites/galleybeggar.co.uk/public_html/wp-content/plugins/wpec-members-nnnnnnnnnnnn/.htaccess pcfg_openfile: unable to check htaccess file, ensure it is readable and that ‘/home/sites/galleybeggar.co.uk/public_html/wp-content/plugins/wpec-members-nnnnnnnnnnnn/’ is executable

After commenting out the four lines in paypal-standard.merchant.php the error no longer comes up, so it seems the error may have something to do with the plugin.

http://wordpress.org/plugins/wp-e-commerce/