Comment # 3 on bug 1074160 from Ju_Ping Chan

Is it possible that this problem is because of a difference between the
repository version of calibre and upstream?

I'm currently using the installation method recommended by upstream which is to
install via 

sudo -v && wget -nv -O- https://download.calibre-ebook.com/linux-installer.py |
sudo python -c "import sys; main=lambda:sys.stderr.write('Download failed\n');
exec(sys.stdin.read()); main()"

Installing from the repositories yields a plugin error, so I stopped using it.