Thanks Kovid, you have of course hit on it. I hadn't realised they were showing because I use tags to identify what is on my Kindle, so when I switched views it was still filtering for the tag. When I turn that off, I can see them in the device view, and the fact that it is not seeing the tag seems to indicate that it is not matching them with the library copy. I suspect that the problem was that I imported them, rather than using the "add books to library" from the device view.
I notice that if I use the "match book to library" function from device view on a book where I have altered the metadata (Amazon have a nasty habit of including series info in the title), I get the "waiting for metadata to be updated" icon, but updating cached metadata does not clear the icon until the device is ejected and reconnected - not a big deal.
