Why didn't I think of this earlier...
Ok try accessing the account from Firefox with the
Firebug addon installed. On the Net panel of that you should see a "POST AutoCompleteRequest" when the ZWC attempts to look up a contact in the compose window. If you click on that line and go to the JSON tab -> Body -> AutoCompleteResponse -> click on one of the numbers. You should see a "type" attribute that tells you were the result came from.
Where are the old results coming from?