System.Timers.Timer や WebBrowser のイベントハンドラーで NullReferenceException 等が起きてもデバッガ

using System;
using System.Windows.Forms;

namespace Hoge
{
    public partial class Form1 : Form
    {
        private System.Timers.Timer timer = new System.Timers.Timer();

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            timer.Elapsed += new System.Timers.ElapsedEventHandler(timer_Elapsed);
            timer.AutoReset = false;
            timer.Interval = double.Epsilon;
        }

        private void timer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            string s = null;
            int a = s.Length;
        }

        private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            string s = null;
            int a = s.Length;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            timer.SynchronizingObject = this;
            timer.Start();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            timer.SynchronizingObject = null;
            timer.Start();
        }

        private void button3_Click(object sender, EventArgs e)
        {
            webBrowser1.Navigate("http://www.atmarkit.co.jp/");
        }
    }
}

    static class Program
    {
        /// <summary>
        /// アプリケーションのメイン エントリ ポイントです。
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }