I haven't tried A8 yet. If TweakMonkey gives problems on MM3A8, then I think that it is because MM doesn't add disabled nodes to the tree (instead of adding but just not showing them).
So if TweakMonkey tries to change visibility of nodes that might not exist (because they are disabled in A8 ), it might give errors or fail silently.
This of course is just a theory.
But it's definately so that, if MM3 can change the tree visibilities by itself, then that function should be removed from TM.