Changing email subject EN_en.php not working

Hi all,

Store URL: http://blackoutbuster.com.au/products-page/
WordPress version: 3.5.2
WP e-Commerce version: 3.8.12.1
Gold Cart version: n/a
Theme: Twenty Eleven

I did this:
edited the EN-en.php file from:
define('TXT_WPSC_ORDER_PENDING_PAYMENT_REQUIRED', 'Order Pending: Payment Required');
to:
define('TXT_WPSC_ORDER_PENDING_PAYMENT_REQUIRED', 'Thank-you for your order!');

I expected WP e-Commerce to do this: Change the email subject when someone places and order

Instead it did this: Nothing.

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