C# LdapException序列化问题-错误代码变为零-.NET错误，还是有意的？

我发现当我序列化和反序列化

System.DirectoryServices.Protocols.LdapException类时，
ErrorCode
属性没有被序列化。我的测试代码如下：

using System;
using System.DirectoryServices.Protocols;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

namespace TestConsole
{
    class Program
    {
        static void Main(string[] args)
        {
            LdapException origExcept = new LdapException(81, "Error code of 81 was set originally.");

            Console.WriteLine("LdapException error code is: " + origExcept.ErrorCode);
            Console.WriteLine("LdapException message code is: " + origExcept.Message);

            // Try independant deep clone
            LdapException ldapClone = (LdapException)deepCloneSerialize(origExcept);
            Console.WriteLine("deep clone error code is: " + ldapClone.ErrorCode);
            Console.WriteLine("deep clone message code is: " + ldapClone.Message);

            // Try binary deep clone
            LdapException binaryClone = (LdapException)binaryCloneSerialize(origExcept);
            Console.WriteLine("binary clone error code is: " + binaryClone.ErrorCode);
            Console.WriteLine("binary clone message code is: " + binaryClone.Message);
        }


        private static object deepCloneSerialize(object obj)
        {
            MemoryStream ms = new MemoryStream();

            DataContractSerializer testSer = new DataContractSerializer(obj.GetType());
            testSer.WriteObject(ms, obj);

            // Now de-serialize and return it
            ms.Seek(0, SeekOrigin.Begin);
            return testSer.ReadObject(ms);

        }

        private static object binaryCloneSerialize(object obj)
        {
            MemoryStream ms = new MemoryStream();

            BinaryFormatter myBinFormat = new BinaryFormatter();
            myBinFormat.Serialize(ms, obj);

            // Now de-serialize and return it
            ms.Seek(0, SeekOrigin.Begin);
            return myBinFormat.Deserialize(ms);
        }
    }
}

该程序的输出如下：

LdapException error code is: 81
LdapException message code is: Error code of 81 was set originally.
deep clone error code is: 0
deep clone message code is: Error code of 81 was set originally.
binary clone error code is: 0
binary clone message code is: Error code of 81 was set originally.

我在3.5和4.0.NET版本的VS 2008和VS 2010中使用了上述两种序列化机制，并且都有相同的结果。奇怪的是，某些方面是正常的，比如异常消息本身，但其他部分不是

那么，我是不是不应该序列化异常（为什么它们被标记为
Serializable
属性？），这是一个症状，还是.NET framework中的一个bug