Global Shopping Cart not adding items when clicked

Hi. I have a marketpress multisite installation and on my main site I have a global product list (generated from a shortcode) that is showing some products. Each product has it's own add to cart button. When I click the add to cart button the button says its been added to that cart but the cart remains empty - it won't populate with the items selected...? I have global cart turned ON and the payment method I selected is paypal express in the network settings. Is something wrong?

On the other hand, when I am on a subsite store page, the cart DOES populate when I click an item's add to cart button. But my cart won't populate when I add an item from the main site's global product lists. Isn't the Global cart feature supposed to add the item? I thought that's what global cart meant.