"Users and Groups" not working properly in Ubuntu 9.10 amd64

1)I created user in installation procedure of Ubuntu 9.10 amd64.
2)After installed Ubuntu successfully, when i tried to access any volume authentication(password) confirmed every time which is default security policy of a user.(no "Users and Groups" changes done until now).
3)To get access to volume without authentication, I have added my user name into "disk","root","sudo","admin" group.
4)Though i am a member of "disk","root","sudo","admin" group,every time authentication is prompted.
5)Then tried to be a user of each group one by one and authentication prompted all the time.Now i am a member of each group,but no use.
6)Then i created one new user and experienced the above things only.
7)Then i deleted that newly created user but i gets appeared in "Login Menu".I ignored it once.
8)Then i restarted the PC,but no change.Then deleted profile folder from home.
9)I restarted my PC again and now also "Login Menu" was showing that deleted user name.I tried to get access that deleted account but an error occurred then i logged in my old account.
10)Then i tried delete that user from terminal,an error was displayed but the entry in my "Login Menu" is deleted now.

Summary: User account do not hold the properties of their group and insecure behaviour of "Users and Groups" experienced in Ubuntu 9.10 amd64.