I've discovered something very very worrying about the urbackup container with btrfs tools,   it's making ghost copies of the container which cannot be deleted, delete the container and image it gives you a warning about being unable to delete a snapshot.   then reboot and there are ghost containers appearing on my dashboard that you can delete, but survive a reboot and are there again.   i am going to message jonp about this, because i'm very concerned that it's doing things to the doc