why shouldn't it work correctly?
Why use it at all? Overprint and Multiply together makes no sense. Just because you can drive your car 240 km an hour doesn't mean you should.
You're using circular reasoning. It's the classic PeeWee arguing technique "I know you are but what am I!".
You're assuming that I want this feature to work out of intentional reasons. Have you given it a second thought that I might want this feature to work in the advent of "accidental" overprint attributes that may come from other people/firms?
Of all people, I'm surprised you are in favor of Adobe NOT fixing a feature they have given us.
IOW, the only problem would be PEBKAC.