StateObject doesn't deinit if I use its @Published vars in View's .alert in iOS15

The StateObject doesn't deinit, if I use it's @Published var in an .alert() in iOS15. Here is the minimal code to reproduce the problem:

@main
struct MyApp: App {
    var body: some Scene {
        WindowGroup {
            MainUIView()
        }
    }
}

struct MainUIView: View {
    var body: some View {
        NavigationView {
            NavigationLink("Go to Child View", destination: ChildView())
        }
        .navigationViewStyle(.stack)
    }
}

struct ChildView: View {
    @StateObject var vm = ChildViewModel()
    
    var body: some View {
        Text("Hello, World!")
        
        //HERE. I have to use $vm.showingAlert from the StateObject:
        .alert("Alert Title", isPresented: $vm.showingAlert, actions: {
            Button("OK") { }
        }, message: {
            Text("Alert Message")
        })
    }
}

@MainActor final class ChildViewModel: ObservableObject {
    @Published var showingAlert = false
    
    init() {
        print("INIT")
    }
    
    deinit {
        print("DE-INIT")
    }
}

If you go to ChildView and back - you won't see "DE-INIT" printed in the console on iOS15. Is it a bug or is my code wrong?

PS Yes I need the showingAlert var to be in the ChildViewModel as it has business logic which shows an Alert in the View.