The above is an anonymous search. Do your acls actually allow results to be returned with anonymous searches?
You may also want to slapcat the DB of both servers and compare. In addition, if the "admin" user is actually only defined in the config database as the rootdn, there's no requirement it exist in the datadb. Since we have no clue what your setup is, we can only shoot in the dark and make random guesses.
--Quanah -- Quanah Gibson-Mount Platform Architect Zimbra, Inc. -------------------- Zimbra :: the leader in open source messaging and collaboration