c# FileLogTraceListener日志类抛错误当修改时间的时候

我的应用使用的是c# FileLogTraceListener日志类记录日志，采用的是多线程，设置LogFileCreationScheduleOption.Daily用来每天生成新的日志文件。记录日志很正常，当我修改系统时间时（即会产生新的日志文件），就会抛出错误，如图所示。
我觉得是个bug，我查看源码能发现当调用CloseCurrentStream()函数时，m_Stream会被设置成null，造成了错误。FileLogTraceListener类在msdn上说的是 线程安全的，看来并非如此。大家觉得是什么原因？

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using Microsoft.VisualBasic.Logging;

namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("start");
Tracelog.StartTrace();

        for (int i = 0; i < 10; i++)
        {
            Thread backthread = new Thread(new ThreadStart(Worker));
            backthread.Start();
        }

    }

    public static void Worker()
    {
        while (true)
        {
            //Console.WriteLine("start");
            Tracelog.Trace(Tracelog.INFO, "test");
            Thread.Sleep(10);
        }
    }
}

public class Tracelog
{
    public static int INFO = 0;
    public static int ERROR = 1;

    public static FileLogTraceListener myListener;

    //private static readonly object Lock = new object();

    public static void StartTrace()
    {
        try
        {
            //lock (Lock)
            {
                myListener = new FileLogTraceListener("myListener");
                myListener.LogFileCreationSchedule = LogFileCreationScheduleOption.Daily;
                myListener.CustomLocation = "log";
                myListener.BaseFileName = "log";
                myListener.MaxFileSize = 10 * 1024 * 1024;
                myListener.WriteLine("Trace start");
                myListener.Flush();
            }

        }
        catch (Exception e)
        {
            Console.WriteLine("StartTrace error" + e.ToString());
        }
    }

    public static void Trace(int type, string message)
    {
        try
        {
            //lock (Lock)
            {
                myListener.WriteLine(message);
                myListener.Flush();
            }


        }
        catch (Exception e)
        {
            Console.WriteLine("Trace error message:" + e.ToString());
        }
    }
}

}

错误信息不完整，特别是第一行，有异常的类型，比如权限不足、无效的操作，等等，具体你看下什么原因。