I've found the reason for this behavior. Here is a patch which correct it. Patch is most probably incomplete. I have no idea what is blkid or libvolume_id but it works.
** Attachment added: "fix for umount'ing volumes mount by user and UUID" http://librarian.launchpad.net/5596114/util-linux_mount.patch -- Can't unmount UUID= volume as a user https://launchpad.net/bugs/71609 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
