site in question: www.nauticalbutnice.tv

i have an inline frame with all the content so that the header and footer stay static on the page. everything works fine until you click on the shop and add an item to your cart. once you've done that, if you click any of the menu buttons the page opens in a new window instead of the frame. like as if the online retailer i'm using somehow changes the name of the frame it opens up in so that the page no longer has a valid target.. does that make any sense? is it even possible for a page to change the name of it's frame? is there any work around this? i don't have full control over the online retailers code so.. not sure what to do here..

thanks!