Dr. Drib -- a limited amount of somewhat-offtopic is normal on MR, and I think this was fairly justified as these things go. It was tangentially related and I would have overlooked it.
tono -- the cover gets downloaded rather than extracted, but as long as there is currently a cover thumbnail ondevice it will not be checksummed and overwritten.
And calibre will automatically sideload one with the book for this exact reason.