uid/gid in question was in the cache, but did not exist
in the password file. This causes the -nouser and -nogroup
options to find(1) to only print the first file owned by
an unknown user/group in some cases.
matter much on some systems, but on ftp servers (like wcarchive) where
you run with special stripped group and pwd.db files in the anonymous
ftp /etc, this can be a major speedup for ls(1).
