[watt]

I do see how it does, in a way. That something the designer thought is "invalid state" turns out a valid and possible state in real world. In terms or UI/UX, it's the uncomfortable long pause before something happens and screen renders (lack of feedback, feeling that system hangs). Or, content flicker when window is resized or dragged. Just because somebody thought "oh, this clearly is invalid state and can be ignored".

The real world and user experience requirements have a way of intruding on these underspecified models of how the world "should" be.

[louthy]

That’s still a poorly designed system. For UI there should be a ‘view model’ that augments your model, that view model should be able to represent every state your UI can be in, which includes any ‘intermediate’ states. If you don’t do this with a concrete and well constrained model then you’re still doing it, but with arbitrary UI logic, and other ad-hoc state that is much harder to understand and manage.

Ultimately you need to make your own pragmatic decisions about where you think that state should be and how it should be managed. But the ad-hoc approach is more open to inconsistencies and therefore bugs.