It has happened to me at least five times. I put a book in french or in latin in my backpack or pants. When I log off and on again, the backpack / pants used to store the book disappear. Random items also disappear such as shoes, gloves, etc. Sometimes both the pants and backpack disappear.

It has never happened to me with a book in english but as I collect french books in game it has happened to me a lot. It has also happened to me the only time I carried a book in latin.