[DoctorOhh]

Originally Posted by HarryT

Note: It's not the "Preferred output format" on the "Behaviour" page. That sets the default format for conversion, but not for saving.

Note: It is the "Preferred output format" on the "Behaviour" page. Change it to azw3 then restart calibre. I just did exactly that and mine now says "Save only AZW3 format."