MarketPress Add to Cart button inside modal

I am setting up a site where products can be viewed either as a full page (e.g. from a search result), or inside a modal (e.g. from a category page).

When a full page, the Add to Cart button works as expected -- it does NOT go to the checkout page.

However, when inside a modal, it DOES go to the checkout page. Is there anyway I can stop that?

Product in modal (going to checkout):
http://demo.accessories-zone.com/model/2013-corolla/
(click on a product to open modal)

Link to product (working as desired):
http://demo.accessories-zone.com/catalog/products/glass-breakage-sensor/

Thanks!