I was also trying to arrange books between the device and storage card today and noticed about 5 strange books.
I had Don Quixote in Spanish, Les Fleur du Mal, French, Eline Vere, French, and a book in German that I managed to delete.
I tried to move them from the device to my PC and an error stated that they were virtual books and could not be moved.
They were all loaded onto the device on 2 May 2012 - well before I got my Glo.
It wasn't really a [rob;em but was just intriguing.