As I said in the post, it is to do with how the engine using the the positioning of reference points. You need to manipulate this to make it work.
I have got your example working by grouping buttons and message and then adding a transparent group between the A Group and the Buttons. This new Group is also hidden when Group B is hidden, and it set to collapse its height when hidden. Now the whole lot move up correctly
I added a note to your demo which states:
“DaveA Says: This problem is fixed by using a transparent group to act as the reference ‘edge’ this is overlayed with the Group B and hidden when Group B is hidden.”
You will find you also need to using things like transparent shapes with 0 minimum size, to act as spacers when using the responsive engine to get layouts to work as expected under certain circumstances.
What i tend to do is leave the shapes coloured while developing, and then when happy how the page works, make the shapes background color none.
Hope this helps!