Redirect to cart broken

I have the reseller plugin installed, and it was working just fine until this week. When you add a product to the cart. it is supposed to redirect to the cart. On a few of the products, it works, but for most of them the results are thoroughly unpredictable. Sometimes it shows the “continue to cart” link, sometimes not. Sometimes it just sits there, and sometimes it redirects to a product post with another “add to cart” button. Sometimes the product post is the right one, sometimes the wrong one. Sometime the product is actually added to the cart (once you navigate there manually), sometimes the cart is still empty.

Is anyone else experiencing this? Or is it just me? I’m on the phone with tech support for the second time this week, on hold right now.

The page I need help with: [log in to see the link]