Yep, thanks Corby. That fixed it.
I had to go through and clean up a few books in the eReader and on the desktop that were in an incorrect state of open or close, but now the eReader does a proper Sync and the desktop app does a proper Update Library. All is well.
I wonder if it wouldn't be a good idea for the many people who don't read this site and are experiencing this fault in annoyed silence, to pop-up a reload suggestion when the desktop is next started up.
ltr