Upfront appears to have broken Marketpress Cart pretty badly

OK so I'm using Upfront Scribe and MarketPress. But I think Upfront has broken the cart very very badly. When you go to the cart it appears to be a static page - it ALWAYS has the same single product on it (not the one you are ordering), you can try and remove that product (it says you have) but it doesn't - as you continue down the purchase path you get to ordering where your correct cart contents show up. I tried removing and rebuilding a product - no change. I think this might have happened when I tried to use Upfront to modify the cart page...as I need the cart and the checkout pages to look something like the Upfront theme I'm using.
But all the documentation about creating marketpress custom-themes is wrong. I cant even find most of the php and css files your documentation points at - perhaps its not kept up with the Marketpress releases? In any case this is REALLY important. If the cart doesn't work that's BAD BAD BAD.