Exchange 2010 combined with Outlook 2010 Service Pack 1 introduced a new “feature” which auto-maps mailboxes you have permissions to in Outlook. This means any mailbox you were granted full access permissions to, Exchange sets an AD link which is used by Outlook to open all mailboxes you have permissions to.
This has really caused a lot of confusion, especially those who are not IT admins but rather employee/owner administrators. To top it all off, removing the permissions do not remove the mailboxes from being visible (even though you don’t have permissions) from your folder view. This is clearly a bug in the design of this “feature.” In most cases, you need to delete and recreate your Outlook profile.