I regularly send books by email to my 11th generation kindle (firmware 5.16.9) using Calibre 7.16.0. It works fine, but when I then connect the kindle directly to the computer via USB, Calibre does not recognise that the book is already available on the kindle.
If I then send the book to the kindle again via USB, I have a duplicate.
I think the effect is relatively new. The problem occurred with one of the last updates. Is the effect known?
