COM Interop: Base class properties not exposed to COM

[Tech quest]

Hi,

I have a C# Class Libarary which is exposed to COM. The issue is base class members are not exposed to COM.As per msdn
http://msdn2.microsoft.com/en-us/library/8877bdk6(VS.80).aspx Managed Clas hierarchies flatten out when exposed as COM objects.
Please let me know how i can resove this issue. Thanks a lot in advance

Here is the sample Application Code:
The issue is base class member properties VehicleName ,Vehicle Type are not exposed to COM

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
 
namespace ClassLibrary5
{
    [Guid("99999999999A-CCCCc-ADDD-73444444E530")]
    public interface IVehicle
    {
        bool Start();
        bool Stop();
        string VehicleName { get; set; }
        string VehicleType { get; set; }
    }
 
    [Guid("4444444444444-1111-5555-44464445FF9")]
    [ClassInterface(ClassInterfaceType.None)]
    public abstract class Vehicle : ClassLibrary5.IVehicle
    {
        private string _VehicleName;
        private string _VehicleType;
 
        public string VehicleName
        {
            get
            {
                return _VehicleName;
            }
            set
            {
                _VehicleName = value;
            }
        }
 
        public string VehicleType
        {
            get
            {
                return _VehicleType;
            }
            set
            {
                _VehicleType = value;
            }
        }
 
        public abstract bool Start();
        public abstract bool Stop();
 
 
    }
}

Derived class:

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
 
namespace ClassLibrary5
{
    [Guid("00000000000-7771-8888-F8487777988")]
    public interface ICar : IVehicle
    {
        string CarType { get; set; }
        int ModelNumber { get; set; }
        bool Start();
        bool Stop();
    }
 
    [Guid("111111111-1234-1234-4567-C5077F131")]
    [ClassInterface(ClassInterfaceType.None)]
    public class Car : Vehicle, IVehicle, ICar
    {
        private int _ModelNumber;
        private string _CarType;
 
        public int ModelNumber
        {
            get
            {
                return _ModelNumber;
            }
            set
            {
                _ModelNumber = value;
            }
        }
 
        public string CarType
        {
            get
            {
                return _CarType;
            }
            set
            {
                _CarType = value;
            }
        }
 
        public override bool Start()
        {
            //Start code goes here
            return true;
        }
        public override bool Stop()
        {
            //stop code goes here
            return true;
        }
    }
}

Thanks,