Price adjustments of attribute not working on variable prices

Hi all

I have a giftcard with some (giftwrap attributes). When I set the price to a fix one for instance 10 EUR and select an attribute ( 3 EUR) , the price becomes 13 EUR.
But when I change the price to a variable one, and let the user set the price (in the textbox) and select a giftwrap attribute) the overall  price  stays unchanged.

am i missing something here ?