Flutter - Widget animation status remains even aft

I'm updating a List<Widget> tiles, but even updating, in which I remove one of the elements of tiles, the state of the animation of the element that came out is still active.

In other words, I redo tiles with this.tiles = buildTile(list); the animation state does not change.

In the example below is removed the Widget that has in its text the string foo3, but its animation continues, and the Widget that has in its text the string foo4 receives this animation.

Is there any way to solve this or is this a bug?

import 'package:flutter/material.dart';
import 'dart:ui' as ui;

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List<Widget> tiles;
  List foos = [];

  @override
  void initState() {
    this.foos = ['foo1', 'foo2', 'foo3', 'foo4'];
    this.tiles = buildTile(this.foos);
    super.initState();
  }

  //function
  List<Widget> buildTile(List list) {
    var x = [];
    for(var i = 0; i < list.length; i++) {
      x.add(
        new ItemCategory(
          key: new Key(list[i]), //new
          category: list[i],
          onPressed: () {
            setState(() {
              list.removeAt(i);
              this.tiles = buildTile(list);
            });
          },
        )
      );
    }
    return x;
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Categories'),
      ),
      body: new ListView(
        padding: new EdgeInsets.only(top: 8.0, right: 0.0, left: 0.0),
        children: this.tiles
      )
    );
  }
}

class ItemCategory extends StatefulWidget {
  ItemCategory({ Key key, this.category, this.onPressed}) : super(key: key);

  final String category;
  final VoidCallback onPressed;

  @override
  ItemCategoryState createState() => new ItemCategoryState();
}

class ItemCategoryState extends State<ItemCategory> with TickerProviderStateMixin {
  ItemCategoryState();

  AnimationController _controller;
  Animation<double> _animation;
  double flingOpening;
  bool startFling = true;

  void initState() {
    super.initState();
    _controller = new AnimationController(duration: 
      const Duration(milliseconds: 246), vsync: this);

    _animation = new CurvedAnimation(
      parent: _controller,
      curve: new Interval(0.0, 1.0, curve: Curves.linear),
    );
  }

  void _move(DragUpdateDetails details) {
    final double delta = details.primaryDelta / 304;
    _controller.value -= delta;
  }

  void _settle(DragEndDetails details) {
    if(this.startFling) {
      _controller.fling(velocity: 1.0);
      this.startFling = false;
    } else if(!this.startFling){
      _controller.fling(velocity: -1.0);
      this.startFling = true;
    }
  }

  @override
  Widget build(BuildContext context) {
    final ui.Size logicalSize = MediaQuery.of(context).size;
    final double _width = logicalSize.width;
    this.flingOpening = -(48.0/_width);

    return new GestureDetector(
      onHorizontalDragUpdate: _move,
      onHorizontalDragEnd: _settle,
      child: new Stack(
        children: <Widget>[
          new Positioned.fill(
            child: new Row(
              mainAxisAlignment: MainAxisAlignment.end,
              children: <Widget>[
                new Container(
                  decoration: new BoxDecoration(
                    color: new Color(0xFFE57373),
                  ),
                  child: new IconButton(
                    icon: new Icon(Icons.delete),
                    color: new Color(0xFFFFFFFF),
                    onPressed: widget.onPressed
                  )
                ),
              ],
            ),
          ),
          new SlideTransition(
            position: new Tween<Offset>(
              begin:  Offset.zero,
              end: new Offset(this.flingOpening, 0.0),
            ).animate(_animation),
            child: new Container(
              decoration: new BoxDecoration(
                border: new Border(
                  top: new BorderSide(style: BorderStyle.solid, color: Colors.black26),
                ),
                color: new Color(0xFFFFFFFF),
              ),
              margin: new EdgeInsets.only(top: 0.0, bottom: 0.0),
              child: new Row(
                mainAxisAlignment: MainAxisAlignment.start,
                crossAxisAlignment: CrossAxisAlignment.center,
                children: <Widget>[
                  new Expanded(
                    child: new Row(
                      mainAxisAlignment: MainAxisAlignment.spaceBetween,
                      children: <Widget>[
                        new Container(
                          margin: new EdgeInsets.only(left: 16.0),
                          padding: new EdgeInsets.only(right: 40.0, top: 4.5, bottom: 4.5),
                          child: new Row(
                            children: <Widget>[
                              new Container(
                                margin: new EdgeInsets.only(right: 16.0),
                                child: new Icon(
                                  Icons.brightness_1,
                                  color: Colors.black,
                                  size: 35.0,
                                ),
                              ),
                              new Text(widget.category),
                            ],
                          )
                        )
                      ],
                    ),
                  )
                ],
              ),
            )
          ),
        ],
      )
    );
  }
}

You need to pass a key to your children. Or else the renderer won't be able to know which SlideTransition got removed, and use the index.

But in your case there's a much easier solution. Use Dismissible

This is exactly what you're trying to do. But already implemented.