Conducting a search of Exchange 2007 email messages on an iOS device results in duplicate results.
This is due to a compatibility issue between the iOS device and Exchange 2007. The device initiates two searches: one server side and the other locally. Since the messages that are synchronized to the device are also on the server, the duplicate results appear. The issue does not exist on newer versions of Exchange, so the only option for a "fix" is to migrate to a newer version.