I get the same result as the other methods of toggling between linear and professional.
I think the problem is that the software considers -both- of the following to be professional, and it auto-converts from the one I want (the first one) to the one I don't.
This seems like a bug since both explicitly exist in the pull-down menu (first image below) and in the Equation Options (second image below), and I explicitly chose the one I want. And I've turned off auto-convert in the Equation Options (third image below).
The bug may be an unwanted auto-convert?
You must be an admin to get Microsoft Technical Support. That person is somebody hidden across a large university campus from me. I will try to find them to get them to report this (apparent) bug.