I wrote an email expressing my dis-satisfaction. I received the following reply"
Our online store links to our live database and is updated automatically approximately every hour. Every once in a while a part might get purchased over the counter at the same time that a part is purchased online, and if we only have 1 unit, the system might not have updated the stock level in time, and the order will be cancelled and refunded in full. I can only assume that's what happened in your case"
Sounds reasonable enough, but the chances of all 7 items purchased at the same time over the counter are remote.