I have a Exchange 2007 user who is using Outlook 2010. When she sends a mail to some one, firstname.lastname@example.org and starts a new mail to that person it brings up the cached address as expected. But once we close Outlook and reopen and try to resend the cached address doesn't appear and the user needs to retype the full address again.
We tested and setup a different Exchange Mailbox on the same machine under a different profile and its Cache works 100%, but not the original one. The weirdness is also on other machines and outlook editions it does the same - once you close Outlook no Cache for that Profile, though other mail Profiles work 100%