Two problems with add_orderby() in query.inc

First of all, the phpdoc indicates a return value, but the function does not return any value.

Second,

     // If grouping, all items in the order by must also be in the
    // group by clause.
    if ($this->groupby) {
      $this->add_groupby($as);
    }
 

This code will add *any* field that's in ORDER BY clause to the GROUP BY clause, however if the field is a formula it shouldn't be added to the GROUP BY clause because then MySQL at least will return an error.