I created a book in Blurb mode and uploaded it. I thought it would be useful to have a PDF version and I switched the Book module to PDF mode. That created the PDFs. But when I tell LR to go back to true book mode, it appears to do so but if I switch out of the Book module and return, the mode is stuck in PDF mode. This change also trashed the last page of the book, deleting it. Closing and restarting LR does not help.