Up button appears on the start destination fragment in Navigation

Question

I have been working on an app and I have hit this problem which I tried to recreate in a demo app. Please have a look at the simple code of this demo app.

ListFragment.kt

class ListFragment : Fragment() {
override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    val binding = DataBindingUtil.inflate<FragmentListBinding>(
        inflater, R.layout.fragment_list, container, false)

    binding.buttonGoToDetail.setOnClickListener {
        findNavController().navigate(ListFragmentDirections.actionNavigateToDetailFragment())
    }

    return binding.root
}

DetailFragment.kt

class DetailFragment : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val binding = DataBindingUtil.inflate<FragmentDetailBinding>(
            inflater, R.layout.fragment_detail, container, false)

        return binding.root
    }
}

MainActivity.kt

class MainActivity : AppCompatActivity() {

    private lateinit var appBarConfiguration: AppBarConfiguration
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
        val navController = navHostFragment.navController

        appBarConfiguration = AppBarConfiguration(navController.graph)
        setupActionBarWithNavController(navController, appBarConfiguration)
    }

    override fun onSupportNavigateUp(): Boolean {
        val navController = findNavController(R.id.nav_host_fragment)
        return navController.navigateUp(appBarConfiguration) || super.onSupportNavigateUp()
    }
}

fragment_list.xml

<layout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">
    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".ListFragment">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:text="@string/description_list_fragment"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            android:layout_marginTop="30dp"/>

        <Button
            android:id="@+id/buttonGoToDetail"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/detail_page_button_label"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            android:layout_marginBottom="30dp"/>

    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

fragment_detail.xml

<layout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">
    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".DetailiFragment">

        <!-- TODO: Update blank fragment layout -->
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:text="@string/description_detail_fragment" />

    </FrameLayout>
</layout>

activity_main.xml

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graph">
    </fragment>

</LinearLayout>

nav_graph.xml

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/nav_graph"
    app:startDestination="@id/ListFragment">

    <fragment
        android:id="@+id/ListFragment"
        android:name="com.example.navigationtest1.ListFragment"
        android:label="list_fragment"
        tools:layout="@layout/fragment_list">
        <action
            android:id="@+id/action_navigateToDetailFragment"
            app:destination="@+id/DetailFragment" />
    </fragment>

    <fragment
        android:id="@+id/DetailFragment"
        android:name="com.example.navigationtest1.DetailFragment"
        android:label="detail_fragment"
        tools:layout="@layout/fragment_detail">
    </fragment>
</navigation>

Problem

Now, when I run the app, it displays the Up button even on the startDestination fragment (which is the ListFragment). I can't figure out why. As much as I understood from the documentation and the codelab tutorial, it should not display the Up button on the startDestination fragment. But, in my case, the Up button appears on the ListFragment and also on the DetailFragment. Though, I must say, the Up button does nothing on the ListFragment page as it is supposed to be.

Any help figuring this out is really appreciated.