problem with emails after paypal payment

Your plugin is fantastic, I have though a little problem with the succesfull payment emails after a paypal transaction. It seems it looses the {purchase_id} in the process. It happens only after a paypal transaction, if I try a manual payment, it works absolutely fine (it gets me the {purchase_id} in both the incomplete and the succesfull payment emails).

Any ideas why?

http://ww.wp.xz.cn/extend/plugins/wp-ecommerce-shop-styling/