[tomsem]

I think Kindles always have generated PDOC cover thumbnails for side-loaded books (assuming cover image is correctly identified as such).

But apparently KCC was marking them as EBOK for older Kindles (Voyage and older) and that meant covers might get removed on those when connecting to Amazon. With that pull request, KCC no longer marks anything as EBOK.

This may not have been obvious before because if you use calibre to side load, it generates cover thumbnails for everything, and restores them if they get removed when you plug in to USB next time (and calibre is running), after which they 'stick'. But none of that is necessary if they are PDOC to begin with.