Using `navigation.navigateUp` incorrectly displays burger menu

Question

I have an activity that is setup to work with Android Jetpack's NavigationUI. This works well and I can navigate correctly except that if I navigate down 2 times, when I navigate up once, the app bar will shows the burger even though there's still one fragment in the childFragmentManager's backstack.

Example:

I navigate to the Alice In Animation RSS feed (this is an RSS reader), then to the Love death & robots article of the feed. Then go back to the articles list. But I'm not yet at the top of the application. There should not be a burger menu here.

Here's my activity class:

class MainActivity: AppCompatActivity() {
    private val navigation: NavController by lazy {
        Navigation.findNavController(this, R.id.main_activity_host_fragment)
    }

    private val drawerLayout by lazy {
        findViewById<DrawerLayout>(R.id.activity_main_navigation_drawer)
    }

    private val drawerToggle by lazy {
        ActionBarDrawerToggle(this, drawerLayout, R.string.navigation_drawer_open, R.string.navigation_drawer_close)
    }

    private val appBarConfiguration by lazy {
        AppBarConfiguration(navigation.graph, drawerLayout)
    }

    private val backstackCount inline get() = main_activity_host_fragment?.childFragmentManager?.backStackEntryCount ?: 0

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        drawerLayout.addDrawerListener(drawerToggle)
        setupActionBarWithNavController(navigation, appBarConfiguration)
    }

    override fun onOptionsItemSelected(item: MenuItem?): Boolean {
        if(item?.itemId == android.R.id.home && backstackCount == 0) {
            val isOpened = drawerLayout.isDrawerOpen(activity_main_navigation_view)
            if(isOpened) drawerLayout.closeDrawers()
            else drawerLayout.openDrawer(activity_main_navigation_view)

            return true
        }
        return super.onOptionsItemSelected(item)
    }

    override fun onSupportNavigateUp(): Boolean {
        val result = navigation.navigateUp(appBarConfiguration) || super.onSupportNavigateUp()
        drawerToggle.syncState()
        return result
    }
}

Here is my navigation graph:

Answer 1

As ianhanniballake commented, NavigationUI handles the home button automatically. ActionBarDrawerToggle shouldn't be used with AppBarConfiguration.