Hi kramps,
they are stored in redis our local database.
- remove your usb stick
- get access to console
- execute this
redis-cli del usbmounts
- check if there are left over folders
ls /mnt/MPD/USB/
- if so, delete them
rm -r /mnt/MPD/USB/foldername
Next time please unmount the usb drive via MENU->SOURCES->USB-UNMOUNTS before removing it.
Frank