when tar dumps and later extracts files without an owner
listed in /etc/passwd it erroneously uses the owner/group of
the last file which had a valid owner. I had to reconfigure
my boot disk and thus dumped its contents with tar,
installed a fresh Redhat 5.2 and restored the data while the
virgin passwd file from the install was in place.

All user files suddenly belong to root because no user
entries exist in /etc/passwd during the restore.

A work around is to use tar's -o option to create old style
archives. Existing tar files may be extraced with the
undocumented option --numeric_owner. The real solution is to
patch the caching in names.c (sent via separate mail).