You're not supposed to get it on pre-orders but it looks like once Zavvi list an item they have to manually disable the code so there's a small window of opportunity to order with the discount.
I've contacted them on some newly released in stock items where it wasn't working and the support staff just send a discount, I'm not sure why they want to make it such a sloppy process.
I'm thinking of holding fire on this release, I expect it'll still have plenty of stock after the release date and get discounted to shift remaining stock, there'll inevitably be a premium release for it and has been pointed out, they got the covers the wrong way round. Maybe it'll be different this time though...