Attempted RemoveListener Bug Repro

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  int? _selectedItem;
  int _currPage = 0;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        body: Builder(
          builder: (context) {
            return SafeArea(
              child: _currPage == 0
                  ? Navigator(
                      onPopPage: (route, result) {
                        if (!route.didPop(result)) {
                          return false;
                        }
                        _selectedItem = null;
                        return true;
                      },
                      pages: [
                        MaterialPage(
                          child: ListView(
                            children: [
                              ScrollAwareWidget(),
                              ...List.generate(
                                30,
                                (index) => TextButton(
                                    onPressed: () {
                                      setState(() {
                                        _selectedItem = index;
                                      });
                                    },
                                    child: Text(index.toString())),
                              ),
                            ],
                          ),
                        ),
                        if (_selectedItem != null)
                          MaterialPage(
                            child: Builder(
                              builder: (context) => Align(
                                alignment: Alignment.topLeft,
                                child: Row(
                                  children: [
                                    IconButton(
                                      onPressed: () =>
                                          Navigator.of(context).pop(),
                                      icon: Icon(Icons.arrow_back),
                                    ),
                                    Text('Selected Item: $_selectedItem'),
                                  ],
                                ),
                              ),
                            ),
                          ),
                      ],
                    )
                  : Container(color: Colors.red),
            );
          },
        ),
        floatingActionButton: FloatingActionButton(
          child: Icon(
              _currPage == 0 ? Icons.navigate_next : Icons.navigate_before),
          onPressed: () {
            setState(() {
              if (_currPage == 0) {
                _currPage = 1;
                return;
              }
              _currPage = 0;
            });
          },
        ),
      ),
    );
  }
}

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

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

class _ScrollAwareWidgetState extends State<ScrollAwareWidget> {
  bool initialized = false;
  late ScrollPosition _position;
  double _scrollProgress = 0;

  @override
  void didChangeDependencies() {
    if (!initialized) {
      print('Initializing ScrollAware');
      initialized = true;
      _position = Scrollable.of(context)!.position;
      _position.addListener(_onScroll);
    }
    super.didChangeDependencies();
  }

  @override
  void dispose() {
    print('Disposing ScrollAware');
    _position.removeListener(_onScroll);
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Text(_scrollProgress.toString(), style: TextStyle(fontSize: 36));
  }

  void _onScroll() {
    setState(() {
      _scrollProgress = _position.pixels;
    });
  }
}