Invalid Response to Response, Links headers when replying to an updated subject line

Question

With the 2013 forecast, if I reply to the email flow when the topic changes, the response does not have the In-Reply-To and References headers.

Not a problem if the object is not modified (then the In-Reply-To and References headers are there as expected)

Not a problem when using Outlook 2007.

Is this a change in the forecast for 2013, setup, error?