Some user names still appear at login

I have updated the default domain group policy to “prevent the display of last user login name” when a user logs into the domain. I refreshed the policy. Now there are some computers that do not show the last user login name (desired result)but there are several computers that continue to show the last user login name (undesired result). These are all XP pro machines with the lastest updates. Any suggestions? Thanks in advance.