"onDetach" not called when UI is detached (after missing 3 heartbeats)

Flow
1

Hello to all,
I’m observing a strange behaviour regarding the onDetach method (I’m using vaadin 10.0.4).

I have a simple RouterLayout with a RouterLink.

@Route("")
public class MainLayout extends Div implements RouterLayout {
    public MainLayout() {
        add(new RouterLink("Test View", TestView.class));
    }

    @Override
    protected void onDetach(DetachEvent detachEvent) {
        System.out.println("calling onDetach method for component " + this);
    }
}

@Route(value = "view", layout = MainLayout.class)
public class TestView extends Div {

    public TestView() {
        add(new TestComponent());
    }

    @Override
    protected void onDetach(DetachEvent detachEvent) {
        System.out.println("calling onDetach method for component " + this);
    }
}

public class TestComponent extends Div {
    @Override
    protected void onDetach(DetachEvent detachEvent) {
        System.out.println("calling onDetach method for component " + this);
    }
}

When I navigate using the link, the onDetach method is called correctly for every children components that are not used anymore,

calling onDetach method for component TestComponent@52f8cbbd
calling onDetach method for component TestView@6b717784

but when the UI is detached (by missing 3 heartbeats), the method is called only for the RouterLayout main component.

calling onDetach method for component MainLayout@366ff498

Is that a bug or a wanted behaviour ?