LimitSubqueryWalker create useless select expressions when "resultVariable" are involved : https://github.com/doctrine/doctrine2/blob/a82f6c5725cb31348eae0b4414e8992b1400ba30/lib/Doctrine/ORM/Tools/Pagination/LimitSubqueryWalker.php#L76-L82

We need to "Preserve mixed data in query for ordering." only if these fields are used in the "order by" clause.