It seems i'am the only guy with double-sided printers ! :cool:
Just had an idea and it solved the problem :
This is the problem : In action.php (in dw2pdf) the defaults are set as
// some default settings
$mpdf->mirrorMargins = 1;
I just removed it from action.php.
If this is needed it must be set in the Acrobat utility and should not be hard-coded.