Hi jazzaj,
But I can still see 'USB Storage (2)' (now it's 2

) on Library tab.
Mpd generates a folder under /mnt/MPD/USB for each device.
So please disconnect your storage and use these commands:
- ls /mnt/MPD/USB
See if there are subfolders, if so:
- rm -r /mnt/MPD/USB/*
- mpc update
From here do not disconnect your storage then the pi is not powerd.
Use remove / delete from the sources tab.
More strange, even if my USB HD is disconnected, I can sometimes 'see' it and browse its folders, files via the USB Storage tab.
This is not strange, it is the normal behavior if you do not update the mpd library.
If unmount your usb media via RuneAudio this is done automatically for you.
Frank