Originally Posted by Wally Bird

It's a simple logic-tree piece of code. Unless some human being simply pores over old itineraries then some piece of code somewhere picked it up post facto.

Now I am prepared to concede that the booking engine code is so complicated in a dogs-dinner kind of way that it's simply too much trouble to reprogram it to detect nesting at source. That's a long way from being impossible; impractical perhaps given the apparent competence of AC's IT department.