You are quoting me. It actually applies to all versions of Word that have the so-called Master Documents "Feature". There is no reason to think it has been fixed. You are welcome to be the test case but I wouldn't recommend doing it with anything that is important to you. I have not tried it in Word 2013.

I have read the published books on Word 2013 and see nothing that gives me any reason to advise someone to put valuable work in this format.