Ajax page-load impeding form action CMS & WordPress

I’m using Zajax plugin for page-loading.

It’s impeding the action of a PayPal add-to-cart form and preventing the desired action and delivering a ‘failed to load’ error.

If I put the form into an iframe, and then remove the form code which was on the page, and replace it with the above iframe, then the button works on Firefox but not Safari – where it’ll add the item to the cart, but not open a new tab and so the user doesn’t know the item has been added.