Back button disappears on NavigationLink SwiftUI

I'm combining a navigation view and a sheet the following way:

struct ContentView: View {
  @State var showingDetail = false

  var body: some View {


  NavigationView {
  VStack {
  NavigationLink(destination: DetailView())
  { Text("Go to view 2") }

  VStack {
  Button(action: {
  self.showingDetail.toggle()
  }) {
  Text("Show Detail")
  }.sheet(isPresented: $showingDetail) {
  SheetView()
  }
  }
  }
  .navigationBarTitle("Back")
  .navigationBarHidden(true)
  }
  }
}


struct SheetView: View {
  var body: some View {
  Text("Detail")
  }
}

The sheet works fine, but the new DetailView when you open it, the Back button seems to be there and then after 1 sec it disappears. How can I fix this?