Downloads do NOT track on Stock ...

You would need to customize the code in the order.php class for:
Code:
          if ((DOWNLOAD_ENABLED != 'true') || $stock_values->fields['product_is_always_free_shipping'] == 2 || (!$stock_values->fields['products_attributes_filename']) ) {
            $stock_left = $stock_values->fields['products_quantity'] - $this->products[$i]['qty'];
            $this->products[$i]['stock_reduce'] = $this->products[$i]['qty'];
          } else {
            $stock_left = $stock_values->fields['products_quantity'];
          }
currently the stock is not reduced on Download Products ...