Zen cart: v1.3.9b

I currently have an issue with the Paypal Express Checkout Module on a certain website. Basically the issue occurs when a user checks out in the normal manner, ie:

- Shipping Address
- Billing Address
- Confirm Order
- Customer sent to Paypal for payment

However, it doesn't matter what shipping address is entered, it is always over-ridden by the address held in Paypal when the order is sent back to the zen cart system.

Is there some sort of flag which needs to be turned on in a payment module file to send the shipping address? Any help would be much appreciated