title: BackHandler not working properly React Native
body: <p>I am trying to go back when the user presses back button on Android.</p>
  
  <p>I have added listener to the screen and it's receiving event when in the remotely debug mode. But it's not working properly when I don't do debug remotely. It's really weird.</p>
  
  <p>I am gonna attach code snippets that I have written.</p>
  
  <pre><code>//Navigator
  const BoardNavigator = StackNavigator({
      Board: { screen: Board }
  });
  
  //Board Component
  class Board extends Component {
      componentWillMount () {
          BackHandler.addEventListener('hardwareBackPress', this._onBackPressed);
      }
  
      componentWillUnmount () {
          BackHandler.removeEventListener('hardwareBackPress', this._onBackPressed);
      }
  
      _onBackPressed () {
          console.log('backPress');
          goBack(this.props.navigation);
          return true;
      }
  
      onNext() {
          this.props.navigation.navigate("Board", {content: ...});
      }
  }
  </code></pre>
  
  <p>Additional Info : 
  This BoardNavigator is the nested one of the rootNavigator(StackNavigator).</p>
  
  <p>react : '16.0.0-alpha.12'</p>
  
  <p>react-native : "0.47.2"</p>