il semble que ca fonctionne avec $state = $this->order->getCurrentState(); dans HTMLTemplateDeliverySlip.php
$state = $this->order->getCurrentState();
if($state == 3){
$this->title = sprintf(HTMLTemplateDeliverySlip::l('Pre-Delivery #%1$s%2$06d'), $prefix, $this->order_invoice->delivery_number);
}
if($state == 4){
$this->title = sprintf(HTMLTemplateDeliverySlip::l('Delivery #%1$s%2$06d'), $prefix, $this->order_invoice->delivery_number);
}