Items from a combined order show as read-only on your customer's page

After you combine two orders, the items that came from the other order no longer show plus and minus buttons on your customer's order page. They are listed as read-only with one sentence: "Added when your orders were combined, so it can't be changed on this page." The remove, swap and replace choices skip those items too. If a customer's old open page still tries to change one, Tacey refuses with a clear message, "This item was added when your orders were combined, so it can't be changed here. Nothing was changed.", instead of a general error. Nothing on the order could be changed before either; the page simply offered a button that could not work.