I realized my error. I had to use the directory where the filesystem is mounted, not the device name. Unfortunately it is not always intuitive when to use what. :-(
The bug report may be closed. -- Mit freundlichen Grüßen Felix Koop -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org