Re: null mounts seem to lose directories?

[nia <nia%NetBSD.org@localhost>]

Also, several older null mounts that appear in df but no longer exist
seem un-unmountable:

# umount -a -t null
umount: /sandbox/nb9-i386-trunk/chroot/16/data: Invalid argument
umount: /sandbox/nb9-i386-trunk/chroot/15/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/14/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/13/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/12/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/11/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/10/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/9/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/8/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/7/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/6/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/5/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/4/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/3/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/2/data: No such file or directory
umount: /sandbox/nb9-i386-trunk/chroot/1/data: Invalid argument

(The output is the same with -f).