Well, not really is it?
Surely Calibre should be written to work with the distributions, not against them.
The distributions already have their own automounters. The purpose of them being that the operating system handles mounting of devices in one centralised way, and that every man and his dog doesn't have to write their "own version" that mounts the devices themselves.
You could argue that Calibre is broken, after all it is trying to mount something that is already mounted. Or because it's working against the standard mechanism to mount a disk.
Letting everything that works with removable storage mount their own storage doesn't make sense: everything would be trying to mount everything more than once, it would become a nightmare.
It would be easy to fix this in Calibre: a "rescan" button that re-examines which devices are available.
The code is probably already in the debug devices section.