Repository: flutter
Issue: NestedScrollView instantaneous jump when body starts to scroll
Labels: framework,f: scrolling,has reproducible steps,P2,found in release: 2.2,found in release: 2.3,team-framework,triaged-framework

```
import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: _title,
      home: MyStatelessWidget(),
    );
  }
}

class MyStatelessWidget extends StatelessWidget {
  const MyStatelessWidget({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final List<String> _tabs = <String>['Tab 1', 'Tab 2'];
    return DefaultTabController(
      length: _tabs.length, // This is the number of tabs.
      child: Scaffold(
        body: NestedScrollView(
          headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
            return <Widget>[
              SliverToBoxAdapter(
                child: SizedBox(
                  height: 250,
                ),
              ),
              SliverOverlapAbsorber(
                handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
                sliver: SliverAppBar(
                  title: const Text('Books'),
                  pinned: true,
                  expandedHeight: 150.0,
                  forceElevated: innerBoxIsScrolled,
                  bottom: TabBar(
                    tabs: _tabs.map((String name) => Tab(text: name)).toList(),
                  ),
                ),
              ),
            ];
          },
          body: TabBarView(
            children: _tabs.map((String name) {
              return SafeArea(
                top: false,
                bottom: false,
                child: Builder(
                  builder: (BuildContext context) {
                    return CustomScrollView(
                      key: PageStorageKey<String>(name),
                      slivers: <Widget>[
                        SliverOverlapInjector(
                          handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
                        ),
                        SliverPadding(
                          padding: const EdgeInsets.all(8.0),
                          sliver: SliverFixedExtentList(
                            itemExtent: 48.0,
                            delegate: SliverChildBuilderDelegate(
                              (BuildContext context, int index) {
                                return ListTile(
                                  title: Text('Item $index'),
                                );
                              },
                              childCount: 30,
                            ),
                          ),
                        ),
                      ],
                    );
                  },
                ),
              );
            }).toList(),
          ),
        ),
      ),
    );
  }
}
```

NestedScrollView shows weird behaviour when some sliver(**SliverToBoxAdapter** in this case) is above **SliverOverlapAbsorber** .
When body starts to scroll slightly, its scroll speed gets faster and scrolls further than expected.
I was able to reproduce this behaviour in several devices.
Above is a reproducible code.

Hope I didn't violate any community rules, since this is my first issuing. Thanks!