Thank You Alki for indicating the problem.
It was a MySql 5.0.5 bug (ORDER BY not working with GROUP BY).
I’ve applyed some changes to ditto.class.inc.pl as posted here
http://modxcms.com/forums/index.php/topic,6320.15.html by funkafize:
edditing assets\snippets\ditto\classes\ditto.class.inc.php line 915
$sql = "SELECT DISTINCT $fields FROM $tblsc sc
LEFT JOIN $tbldg dg on dg.document = sc.id
WHERE sc.id IN (" . join($ids, ",") . ") $published AND sc.deleted=$deleted $where
".($public ? ’AND (’.$access.’)’ : ’’)." GROUP BY ".($sort ? " $sort " : " sc.id ") .
($sort ? " ORDER BY $sort" : ""). " $limit ";
the bold part was : ".($public ? ’AND (’.$access.’)’ : ’’)." GROUP BY sc.id" . --->So always was grouping by id
Right now sorting works prefectly.
PROBLEM SOLVED !