home: Meet a bug seems type inference error

Hi, I meet an “InvalidCastException” when deserializing the serialized content to my data model, it seems that there is incorrect type inference, this is the details of the exception:

System.InvalidCastException HResult=0x80004002 Message=Unable to cast object of type ‘ExtendedXmlSerializerTest.Backend’ to type ‘ExtendedXmlSerializerTest.WorkerBackend’. Source=<Cannot evaluate the exception source> StackTrace: <Cannot evaluate the exception stack trace>

and this is my data model:

{
	public class Backend
	{
		public string Host { get; set; } = "localhost";
		public int Port { get; set; } = 8080;
	}
	public class Portal
	{
		public string Name { get; set; } = "portal";
		public Backend Backend { get; set; } = new Backend();
	}
	public class WorkerBackend
	{
		public string ServerUrl { get; set; } = "http://localhost:8080";
	}
	public class Worker
	{
		public string Name { get; set; } = "worker";
		public WorkerBackend Backend { get; set; } = new WorkerBackend();
	}

	public class Config
	{
		public Portal Portal { get; set; } = new Portal();
		public Worker Worker { get; set; } = new Worker();
	}
}

my serializer implementation:

using ExtendedXmlSerializer.ExtensionModel.Content;
using ExtendedXmlSerializer.ExtensionModel.Xml;
using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Xml;

namespace ExtendedXmlSerializerTest
{
	public static class ConfigSerializer
	{
		public static Config LoadConfig(string filePath)
		{
			IExtendedXmlSerializer serializer = new ConfigurationContainer()
				.Ignore(typeof(List<>).GetProperty(nameof(List<object>.Capacity)))
				.UseOptimizedNamespaces()
				.Create();
			using (var stream = new StreamReader(filePath))
			{
				return serializer.Deserialize<Config>(stream);
			}
		}
		public static void SaveConfig(Config config, string filePath)
		{
			var serializer = new ConfigurationContainer()
				.Ignore(typeof(List<>).GetProperty(nameof(List<object>.Capacity)))
				.UseOptimizedNamespaces()
				.Create();
			var content = serializer.Serialize(new XmlWriterSettings
			{
				NewLineChars = Environment.NewLine,
				Indent = true,
				IndentChars = "  ",
				Encoding = Encoding.UTF8,
				DoNotEscapeUriAttributes = true
			}, config);
			File.WriteAllText(filePath, content);
		}
	}
}

and this is my test code:

static class Program
	{
		static void Main(string[] args)
		{
			Console.Write("input file name: ");
			var fileName = Console.ReadLine();
			var config = new Config();
			ConfigSerializer.SaveConfig(config, fileName);
			var config2 = ConfigSerializer.LoadConfig(fileName);
			Console.WriteLine($"portal backend: http://{config2.Portal.Backend.Host}:{config2.Portal.Backend.Port}");
			Console.WriteLine($"worker backend: {config2.Worker.Backend}");
		}
	}

Could anybody help me whether I’m using it the wrong way or something I missed? Thanks.