Make sure that menu Parameters (Advanced) are set as:

Category Order: No Order by Primary Order Only
Primary Order: Most Recent First

Open file .../components/com_content/helpers/query.php.

Change the following, about line 50.

function orderbySecondary($orderby)
 {
 switch ($orderby)
 {
 case 'date' :
 $orderby = 'a.created';
 break;

 case 'rdate' :
 $orderby = 'a.created DESC';
 break;

Change value underlined in:

function orderbySecondary($orderby)
{
switch ($orderby) 
{
case 'date' :
$orderby = 'a.publish_up';
break;

case 'rdate' :
$orderby = 'a.publish_up DESC';
break;

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