Well, well, turn of events! After receiving the order I triple checked the order and also phoned Apple to make 100% sure we had not ordered the extra iPad. It was not listed anywhere on our account, something that was confirmed by one of their sales execs. However, we received our invoice today and they have charged us for it! Seems a weird error and no one at Apple can offer any explanation as to what happened. Upshot is that it's going back! Good job I hadn't given it away yet.