For future googleers with the same problem, the solution was to rename the mount point to something random which 'Unassigned Devices' allows you to do with a single click on the mount point name situated just under the disk name.
I'm trying to copy across some data via USB disks using Krusader and Unassigned Devices. Unfortunately, when I click the mount button it's wheels spin and nothing happens.
It's bewildering. Any thoughts appreciated.