Disclaimer: I'm only speaking from what I observed, not from any place of inside knowledge. So this is all speculation, not absolute truth.
If they're not persistent they just don't exist until they get a value. If they have a binding, it gives them a value, so they stay around.
I think you can try to put a binding on a prop, disable the binding, then make disable its persistence.
Close the view, reopen it, the prop is gone. Re-add a prop with the same name, and you'll see it still has the disabled binding.