Cloning a query object re-creates hydrator object and loses hydration mode in the process.

This is obviously wrong since cloning should result in identical object, but why this is such a critical bug is because it breaks setting array hydration for nested set base query, because the query object gets cloned during the fetching of tree. This bug was introduced in revsion 6691 in attempt to fix DC-204. Included is a patch that correctly clones the hydrator instead of resetting its information completely.