Cant buy giftcard and product at same time

I have a problem when it comes to gift card. If i add a product to cart and after that i add a gift card, follow the instruction to checkoutpage, it get a error (something about shipping).

So basicly when i add a gift card, the checkout page ignore shipping, even when i have other products in the cart that requires shipping. This result in a error.

Is this a Opencart bug (im using 1.5.1) or is this related to my theme?

Tried to do the same in OC 1.5.3 and this do not result in a error. Will upgrade my store to 1.5.3 now