DesiredFocusWidget serialized in instances, but editable only in defaults

UPROPERTY(EditDefaultsOnly, Category = "Interaction", meta = (AllowPrivateAccess = "true"))
FWidgetChild DesiredFocusWidget;

I have MainMenu UserWidget, then I create Popup UserWidget.
Whenever I open my Popup I set focus to it and learn I want to focus on one of it’s buttons, so I open Popup and set it focusable and DesiredFocusWidget to a button inside of it.

But it doesn’t change behavior in MainMenu’s popup, because it’s overriden and not accessible at the same time >:[

If something is [EditDefaultsOnly] it shouldn’t serialize in instances. Why do I have to delete Popup from MainMenu and place it again!?

{
	"Tagged": [
		[
			"bIsFocusable",
			"True"
		],
		[
			"DesiredFocusWidget",
			"(WidgetName=\"\")"
		]
	]
}

This is what is saved in instance.

But I also had similar problem with Button UserWidgets in Popups, and changing “DesiredFocusWidget” applied correctly to Popup.

Maybe the problem is toggling IsFocusable? Does it dirty entire category?