If you attempt to add a user and manually specify a UID less than 500, you're prompted to confirm your UID choice. If you say "yes", everything works as expected. However, if you say "no", the dialog hangs -- it goes grey and gives you the busy cursor forever. This is in the latest 1.2.12-3 devel package, and I just checked on RHL 9, and it's there in redhat-config-users-1.1.5 as well. I'd mark this as Severity High, since it hangs the program reliably, but apparently no one else has ever had this problem. Am I the only one who looks at this package? *grin*
Should be fixed in system-config-users-1.2.12-5 in Rawhide. Thanks for your report.