Gridmarket - Randomly stopped being able to empty cart

Hey,

One of my clients has told me that suddenly (or near enough) her customers are unable to empty their carts.

I can replicate it as its not working for me now.

Here is the page. http://customtabs.co.nz/shineon

To replicate:

Add item to cart.
Remove it via the cart widget.

Also when you add an item to the cart, it takes you to the checkout page instead of loading it into the cart via AJAX.

Can you please advise?

Ben