When "out of stock" isn't possible

Earlier today I placed a rather large book order with Overstock.com having found some rather decent prices on some items that have been on my Amazon.com wishlist for a while now. I also pre-ordered three titles since Overstock.com was offering them at a more significant discount than other online retailers.

A few hours went by and I received three e-mails informing me that some of my items had been canceled since they were "out of stock". Trouble was, the canceled items are all the pre-orders. Huh?

So, off I go to their online customer service to have the following conversation:

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Welcome to Overstock.com's Customer Service Live Chat! You will be joined with a chat representative as quickly as possible. (Less than 2 minutes)
Welcome to Overstock.com Customer Service, you are now chatting with Alexa.
Alexa: Thanks for visiting Overstock.com, this is Alexa, how can I help you?
you: I just received three refunds for books I ordered earlier today. The reason given on each was that you're "unable to ship the item." In each case, the book was a pre-order since it's not out yet. Therefore I expected the books not to be shipped until their release dates. Why were the orders canceled?
you: Order Number: 68166031
Alexa: Let me check and help you with the information.
Alexa: For security purposes, can you please verify the name and billing address on the account?
you: Michael Sauers, ...
Alexa: Just to confirm, are you referring to the 'Torchwood 2009 Yearbook', 'The Complete Star Wars Encyclopedia (Hardcover)' and the 'The Torchwood Archives (Hardcover)'?
you: Yes
Alexa: Thank you for verifying the information, Michael.
Alexa: Unfortunately, the item ordered is no longer in stock. Since we deal in the liquidation of merchandise, products featured on our site tend to sell out quickly. Still, we should not have taken an order for an item we are unable to ship.
Alexa: We use an inventory control database to prevent this from happening, but some error has apparently occurred in the process. I'm terribly sorry for the inconvenience that this error on our part has caused you.
you: How can it be "out of stock" if it's not out yet and only available for pre-order?
Alexa: I understand that all the 3 items are Pre-order items.
Alexa: However, our warehouse has confirmed that we wouldn't be able to ship these 3 items as they are out of stock.
you: "out of stock" assumes you had stock in the first place which is impossible since the books have not yet been published.
Alexa: I do understand, however, after accepting the orders our warehouse has confirmed that these 3 items cannot be shipped.
you: thanks, I guess...
Alexa: Thanks once again for the opportunity to help you. At the same time, I'm also sorry that you were put through inconvenience about this issue.  
Alexa: I’m happy to help. Do you have any further questions for me?
you: No.
Alexa: Thanks for visiting Overstock.com. Have a great day, bye.
Chat session has been terminated by the Overstock Service representative.

Yeah, that totally explains it. If you can't ship an item, just apologize and let everyone move on. Don't insult my intelligence by giving me an impossible explanation. Sorry Overstock.com, you just lost a customer and got this blog post in return.