Index: branches/5.2.x/units/orders/orders_event_handler.php
===================================================================
--- branches/5.2.x/units/orders/orders_event_handler.php
+++ branches/5.2.x/units/orders/orders_event_handler.php
@@ -2983,7 +2983,7 @@
 
 			$processed_sub_orders[] = $sub_order->GetID();
 
-			$next_sub_number++;
+			$next_sub_number = $sub_order->getNextSubNumber();
 			$group++;
 		}