account won't delete even when clicking delete

[Jet]

Binary package hint: adduser

Buggy program: User and Groups (System->Administration->User and Groups)
Package: adduser

I tried to delete my old user account. I was trying to delete my old account "jet" with User and Groups using my new account "j" and the user "jet" disappears on the list. My old and new user accounts has admin privileges. When I click User and Groups again, the user account "jet" is still there. I restarted the computer which I hope the problem would be fixed. When I reopen User and Groups, "jet" was still there. I try to delete the account using the terminal but it gave me this error message, "userdel: unable to lock password file". Then, I deleted /home/jet/. The user account "jet" still exist but its home folder was deleted.

To reproduce:
1. Open User and Groups
2. Delete the user account "jet"
3. Close User and Groups
4. Reopen User and Groups
5. Restart the computer
6. Open User and Groups again

Ubuntu release version:
Description: Ubuntu 9.04
Release: 9.04

[dumas33 (danas-augutis)]

I have same problem in 9.10. Cant delete other user. after unlocking, deleting, closing users setting and reopening it user appears again.