C# BackgroundWorker的Bug？？？

废话不多说，上代码:

public partial class Form1 : Form
    {
        BackgroundWorker _bgWorker;
        int count;

        public Form1() 
        {
            InitializeComponent();

            _bgWorker = new BackgroundWorker();
            _bgWorker.WorkerReportsProgress = true;
            _bgWorker.WorkerSupportsCancellation = true;
            _bgWorker.DoWork += _bgWorker_DoWork; ;
            _bgWorker.ProgressChanged += _bgWorker_ProgressChanged; ;
            _bgWorker.RunWorkerCompleted += _bgWorker_RunWorkerCompleted;
            timer1.Enabled = true;
        }
                
        private void toolStripButtonStart_Click(object sender, EventArgs e)
        {            
            count = 0;
            _bgWorker.RunWorkerAsync();
        }

        private void toolStripButtonStop_Click(object sender, EventArgs e)
        {
            _bgWorker.CancelAsync();

            // 加上这三行代码就会导致不能触发_bgWorker_RunWorkerCompleted，_bgWorker.IsBusy一直未true阻塞在这个地方
            while (_bgWorker.IsBusy)
            {
                Thread.Sleep(100);
            }            
        }
        
        private void _bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            System.Windows.Forms.MessageBox.Show("Test Done");
        }

        private void _bgWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            toolStripLabelIsRunning.Text = count++.ToString();
        }

        private void _bgWorker_DoWork(object sender, DoWorkEventArgs e)
        {
            BackgroundWorker bgWorker = sender as BackgroundWorker;
            bool boolFlag=false;
            while (!bgWorker.CancellationPending)
            {
                Thread.Sleep(100);
                boolFlag = !boolFlag;
                if (boolFlag)
                {
                    bgWorker.ReportProgress(1);
                }
            }

            Debug.WriteLine("Successfully Exite");
        }       
    }

在一个简单的form中添加一个BackgroundWorker，并注册DoWork，ProgressChanged，RunWorkerCompleted事件

在如图中toolStripButtonStop_Click 界面响应事件函数中如果没有加以下三行代码一切运行正常，Start后正常运行，Stop后正常的推出并触发RunWorkerCompleted事件，

           while (_bgWorker.IsBusy)

           {

               Thread.Sleep(100);

            }

但是如果toolStripButtonStop_Click 界面响应事件函数中加入了这三行代码则RunWorkerCompleted事件永远都不会被触发，_bgWorker.IsBusy永远都是true导致toolStripButtonStop_Click 界面响应事件函数无法退出（实际上_bgWorker_DoWork函数早就已经退出了，在输出窗口中可以看到_bgWorker_DoWork函数退出前运行了 Debug.WriteLine("Successfully Exite"); 输出的Successfully Exite字符串）

请教各位大神，这是为什么？？？