Here is the workaround:
echo -e '#!/bin/sh\nexit 1' > /usr/bin/calibre-mount-helper ; chmod +x /usr/bin/calibre-mount-helper
and here is a quote from a Linux developer about this:
We rely on the desktop's automounting for ebook storage volumes. Quite frankly, calibre-mount-helper is really not appropriate to ship, it's by and large an unsafe rewrite of the much better understood mechanisms that udisks and even hal already provide. It's not necessary for calibre to work either, once the OS automounts the storage volumes they will just appear automatically in calibre's UI.
So calibre just needs to drop the calibre-mount-helper program for distros that use udev