not adding to cart in IE but works in other browsers

i have a store running thought a facebook app.

here is a working example.

http://www.facebook.com/pages/Custom-Tabs-Store-Front-Example/177200529034879?sk=app_139913369442307

i am having a major deal breaker problem.

when i add to cart in IE (all versions), it doesnt actually register anything in the cart. but it works fine if you open the cart url in its own tab/window.

i have no problems in any other browser.

please test and advise