2 days ago when I checked my WL, I had a book on their that the system said was last posted 11-02-2010.  Now the system is consistently showing that it has never been posted.

Is this because this info is tied to members (maybe the member who posted the book went on vacation hold), or is it just a glitch.  Does anyone know.

Somebody asked about this previously, and the answer from PBS was that the book is no longer being tracked by the system. In this case, it sounds like it was marked received, and the user chose not to put it on his/her TBR list or bookshelf.

The last posted date uses the data of books on PBS bookshelves.  If you check the option to not have the book on hold on your bookshelf when checking the book in, then the data goes away.