Send on Behalf of Issues in Outlook 2007

I have 2 users here (User A and User B) whom I am supporting. These users do not have access to the other’s Outlook resources (Inbox, calendar, etc.). However, user B now has “send on behalf of” permissions for the other. They aren’t delegates for each other and the “send on behalf of” permissions haven’t been granted for either users in Active Directory.

Any ideas or suggestions as to how I can resolve this?