Index: branches/version-2_11-dev/data/class/pages/admin/order/LC_Page_Admin_Order_Edit.php
===================================================================
--- branches/version-2_11-dev/data/class/pages/admin/order/LC_Page_Admin_Order_Edit.php	(revision 20981)
+++ branches/version-2_11-dev/data/class/pages/admin/order/LC_Page_Admin_Order_Edit.php	(revision 20982)
@@ -739,4 +739,5 @@
             if ($exists_product_class_id == $product_class_id) {
                 $exists = true;
+                $exists_no = $key;
                 $arrExistsQuantity = $objFormParam->getValue('quantity');
                 $arrExistsQuantity[$key]++;
@@ -768,5 +769,5 @@
                 $objFormParam->setValue($key, $arrValues);
             }
-        } elseif (isset($changed_no)) {
+        } elseif (isset($changed_no) && $exists_no != $changed_no) {
             // 変更したが、選択済みの商品だった場合は、変更対象行を削除。
             $this->doDeleteProduct($changed_no, $objFormParam);