Adding a ZStack around a TabView/NavigationView moves content up into safe area when .blur is used

Question

My application uses a TabView and contained in it there is a NavigationView so I can transition to different views on the selected tabs. I am using .navigationTitle together with .navigationBarTitleDisplayMode(.large) to show users where they are (in the example below the title is set to "Pfizer"). All is working fine as you can see below:

    var body: some View {
        TabView(selection: $selectedTab) {
            NavigationView {
                ...

However, as soon as I put a ZStack around the TabView (or use .overlay) the entire views including the navigation header move up into the safe area even though I have not specified an .ignoresSafeArea anywhere! Here is how it looks like when I am using ZStack around it:

    var body: some View {
        ZStack(alignment: .center) {
            TabView(selection: $selectedTab) {
                NavigationView {
                    ...

Note that I intend to use ZStack to conditionally show a view on top of my TabView/NavigationView as follows:

    @Binding var condition: Bool

    var body: some View {
        ZStack(alignment: .center) {
            TabView(selection: $selectedTab) {
                NavigationView {
                    ...
               }
            }
            .blur(radius: condition ? 3 : 0)
            if condition {
                VStack {
                    VStack(alignment: .center) {
                        Text("Some text")
                            .font(.title2).padding(.bottom)
                    }
                    .padding()
                    .background(Color(.secondarySystemBackground))
                }
                .padding(.horizontal, 40)
            }
        }
    }

I managed to figure out by trial and error that the problem only occurs if I am using the .blur view modifier on the TabView that is inside the ZStack. If I remove the .blur view modifier, then the problem that I described does not occur and so the initial comment of Asperi makes sense.

I do not understand this behavior and I have no idea why using .blur messes up the safe area. Can anybody explain this behavior to me please?