reproducing https://github.com/flutter/flutter/issues/11895

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(
    home: new DefaultTabController(
      length: 3,
      child: new SafeArea(
        child: new Scaffold(
          bottomNavigationBar: new Container(
            child: new TabBar(
              labelColor: Colors.black,
              labelStyle: TextStyle(fontSize: 20.0),
              tabs: [
                Text('foo'),
                Text('bar'),
                Text('baz'),
              ]
            ),
          ),
          body: new TabBarView(
            children: [
              new FooPage(),
              new BarPage(),
              new BazPage(),
            ]
          )
        )
      )
    )
  )
  );
}

class FooPage extends StatefulWidget {
  @override
  FooState createState() => new FooState();
}

class FooState extends State<FooPage> with AutomaticKeepAliveClientMixin<FooPage> {
  @override
  bool get wantKeepAlive => true;

  @override
  Widget build(BuildContext context) {
    return new Center(
      child: new Text('foo')
    );
  }
}

class BarPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Center(
      child: new Text('bar')
    );
  }
}

class BazPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Center(
      child: new Text('baz')  
    );
  }
}