Beginner question: "Hold"-notes stops when changing Part

[Kai-vD]

Not in Stack-Mod:

When I have "Hold"-notes" in one part, and then change to edit the other part, the held-notes from the first part stop playing. Why is that so? What is that good for?

While performing and having held-notes in one part, I would of course want these notes continuing playing when I want to tweak a parameter of the other part. Or what do I get wrong?