Our warehouse is still working their way through the high volume of orders that were placed when the DVD was added to the store in July. They haven't gotten to the orders from August 4 yet. As such, we're considering the DVD to be a special case -- it's not "in stock" yet, but still considered to be on preorder / backorder until all of the initial orders have been fulfilled.
We do tell you in the cart when an item is backordered, and it says on the store pages where the disc can be ordered that it's in preorder status with an expected ship date of sometime in August. Don't worry, your order will ship when they get to it in the line!