So, it seems that ebook users need to add a new word to their vocabulary: “undownloading” — what happens when you leave the authorized zone in which you may read the ebooks you paid for, and cross into the digital badlands where they are taken away like illicit items at customs. If you are lucky, you will get them back when you return to your home patch — by un-undownloading them.
via Techdirt

Added.
Consider this was a physical book, you would be fined for smuggling books that you have legitimately brought or your books taken under protective custody by someone, after all they contain the most dangerous things known to humans – ideas!