Flutter EventChannel onCancel is not called on Activity destroy

main.dart

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  LongRunningPlugin _plugin = new LongRunningPlugin();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: StreamBuilder(
          initialData: "0",
          stream: _plugin.getIt,
          builder: (context, snapshot) =>
              Text('Non-canceled tasks: ${snapshot.data}'),
        ),
      ),
    );
  }
}

class LongRunningPlugin {
  final EventChannel channel = EventChannel("long_running_plugin");
  Stream get getIt => channel.receiveBroadcastStream();
}

MainActivity.java

public class MainActivity extends FlutterActivity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    LongRunningTaskPlugin plugin = new LongRunningTaskPlugin();
    EventChannel channel = new EventChannel(getFlutterView(), "long_running_plugin");
    channel.setStreamHandler(plugin);
  }

  static class LongRunningTaskPlugin implements EventChannel.StreamHandler {
    @Override
    public void onListen(Object args, EventChannel.EventSink eventSink) {
      Log.i(TAG, "onListen");
      eventSink.success(++counter);
    }

    @Override
    public void onCancel(Object args) {
      Log.i(TAG, "onCancel");
      counter--;
    }

    private static int counter = 0;
    private static final String TAG = "LongRunningTaskPlugin";
  }
}