If you mount your phsycally mounted USB's directory for NFS/CIFS content will play properly, but if you use non existend device than it makes problem.
I don't know why it's happenning actualy. TV not recognize that `mounts` at that way an require real device attached on port. I think could be work around using loop device.
But leavi'ng a usb stick on port is better solution for now.
