Running Debian 9 with cinnamon desktop on a T440p Thinkpad leads to the described results.
Kernel Version 4.9.0-8-amd64 SMP Debian 4.9.130-2 cinnamon Version 3.2.7-4 nemo Version 3.2.2-3 On an USB 2 Port mounting, unmounting and power off commands from cinnamon desktop / filemanager nemo work On an USB 3 Port Mounting and unmounting commands from cinnamon desktop / filemanager nemo work. Power off leads to system hang. Regards Martin