> It is the same reason. The umount command tries to access the
> old mountpoint and fails because that mountpoint is invalid.
> 
> You can use the 'umount -R' command to bypass "all attempts to
> be smart about mechanically determining the correct path from
> the argument".

*sigh* It also does not work in this case:

# mount | grep stuffy
flam:/stuffy on /flam/stuffy type nfs (read-only, nosuid, nodev)
# umount -R flam:/stuffy  
umount: flam:/stuffy: No such file or directory
# umount -fRv flam:/stuffy
flam:/stuffy: unmount from flam:/stuffy
umount: flam:/stuffy: No such file or directory
# umount -fRv /flam/stuffy
/flam/stuffy: unmount from /flam/stuffy
umount: /flam/stuffy: Invalid argument