There is a WD script that is reseting them
to what is set in the WD Web Interface for each share and its media sharing type
On the WD MBL I rename this file to deal with the issue
/usr/local/sbin/writeTwonkyContentDir.sh
I know that on the WD Mycloud there is something similiar going on
in the past i was helping someone with this issue on WD Mycloud
the issue is an extra thing that is going on with it in regards to usb mounted drives
the post was on a forum that no longer exists, so I dont have anything to reference for you
you basically have two options
Option 1.
use the wd web interface for folder sharing and define the media sharing you want on those shares there
Option 2.
rename the script I referenced above, restart twonky or the nas
and use the twonky web interface to define your media shares
