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).
added patch and rebuilt for next release. currently in rawhide.