> Yes, that's the intended behavior, if you have a group selected then an edit works on the whole group including hidden sub objects.
> That's the same behavior as other programs that use groups, like Affinity Designer or Inkscape for example.

Well, I'll have to disagree with Affinity Designer and the whole rest of the world because it is an opaque convention, especially to the uninitiated.
Mio has a smoother learning curve than most every other software. That's a big reason it so beloved (IMHO).