Hi,
I've found a solution from this topic http://forum.pfsense.org/index.php/topic,9016.msg51238.html#msg51238.
After changing line 1017 in /etc/inc/filter.inc from:
$after_filter_configure_run[] = "/usr/local/sbin/pftpx {$shaper_queue}-f {$target} -b {$external_address} -c 21 -g 21";
to:
$after_filter_configure_run[] = "/usr/local/sbin/pftpx {$shaper_queue}-f {$target} -b {$external_address} -c 21 -g 21 -r";
it works as expected.