Weird address' resolving problem

I have 2 users here at my work that are having the same problem. When they create a new e-mail and begin typing in a name in the To: field they hit tab and the name resolves from our global address list, but also a contact from their personal contacts with the same first name appears.

For example, they type in "Smith" hit tab and it resolves to "Smith, John" from our global address list, then it also adds a "John Davis" from their personal contacts.

I did some research and found their to be a database with all the nicknames (.nk2), I've removed that file and let Outlook recreate it, but the problem comes back. Does anyone know of any fixes for this?

We are using Outlook XP with Exchange 5.5.

Thanks

Nobody has ever come across this problem? Anyone know of a better discussion group I should post this question at?