https://github.com/AutoMapper/AutoMapper/issues/2095

gistfile1.txt

using System;

namespace ClassLibrary1
{
    public interface I
    {
        int MyProperty { get; set; }
    }

    public class IA : I
    {
        public int MyProperty { get; set; }
    }

    public class IB : I
    {
        public int MyProperty { get; set; }
    }

    public class MyType
    {
        public I Interface { get; set; }
    }

    public class Program
    {
        public static void Main( string[] args )
        {
            var source = new MyType() { Interface = new IB() { MyProperty = 1 } };

            AutoMapper.Mapper.Initialize( cfg => {  } );
            var target = AutoMapper.Mapper.Map<MyType>( source );

            bool result = Object.ReferenceEquals( source.Interface, target.Interface );
        }
    }
}