MarketPress Add to Cart button fails with new WP 3.7

I just updated WP to version 3.7. While checking the site I saw that the "Add to Cart" shortcode button I have on the homepage doesn't work any more. When clicking on it, the notice "items added" fades in and out, the button disappears, but also does not add product to the cart.

The "Add to Cart" button on the product page works. It's just the shortcode.

Site link:

Thanks for your help.