Im guessing this is under shadow-utils, but who reall knows :) The problem is this: userdel will segfault and dump core if you try to remove a user that doesn't have a GID listing in /etc/group. I have only experienced this problem on RH 6 systems, but I also don't have access to previous releases. I was able to test this on an old slackware machine, and it was unaffected
This seems to be working in the lastest release of shadow-utils that is available from our ftp site. ftp://ftp.redhat.com/pub/rawhide/i386/RedHat/RPMS/shadow-utils-19990827-2.i386.rpm