C#/VS2013-为什么此代码在未调试的情况下失败

下面是我为测试基本线程场景而编写的一个程序。当我在启用调试的情况下运行它时，它的工作方式与预期完全一样。

using System;
using System.Threading;
class Program
{
    static bool keepCounting;
    static void Main(string[] args)
    {
        Thread myThread = new Thread(countNumbers);
        myThread.Name = "MyThread";
        keepCounting = true;
        myThread.Start();
        Thread.Sleep(new TimeSpan(0, 0, 1)); // countNumbers() runs for 1 sec.
        keepCounting = false;
    }
    static void countNumbers()
    {
        Console.WriteLine("{0} beginning count.", Thread.CurrentThread.Name);
        long n = 0;
        while (keepCounting)
        {
            n++;
        }
        Console.WriteLine("Current thread:          {0}", Thread.CurrentThread.Name);
        Console.WriteLine("Number of iterations:    {0}", n);
    }
}

然而，当我将VS设置为进行发布构建，并使用"Start Without Debugging"运行它时——请注意，这两个步骤都必须执行，否则它仍然会成功——在打印"MyThread starting count."后，它神秘地被"卡"在countNumbers()方法中间的某个位置，并且它从未超时并将结果打印到控制台窗口。

有人能解释这种怪癖吗？

while (keepCounting)
{
    n++;
}

var cpu_register = keepCounting;
while (cpu_register)
{
    n++;
}