Have you brought this to their attention? Every edition/format of the book should have a different ISBN number. Selling multiple editions under one ISBN could mess up a lot of things. For example, if as an associate I wanted to put a link to your 2005 edition on my site, I wouldn't be able to, as it would always resolve to the 1981 edition. I assume they ask for the ISBN when you start selling a book.
This isn't their usual operating procedure. When I do a search for a particular DVD, along with the current version it'll often bring up several defunct editions because someone's selling a copy or two. Any edition that's available for sale - by anyone - on the site should show up. (In fact, it's not unusual for an un-available version to come up in a search.)
[edited by: Beagle at 11:26 pm (utc) on July 29, 2008]