ServiceStack.Text Deserializer Issue

main.cs

using System;
using System.Linq;
using ServiceStack;
using ServiceStack.Text;
using System.Collections.Generic;

public class Request
{
    public bool? IsOk {get; set;}
}

var req1 = "{\"IsOk\": \"fu\"}".FromJson<Request>();
var req2 = "{\"IsOk\": \"ere\"}".FromJson<Request>();
req1.PrintDump();
req2.PrintDump();

packages.config

<?xml version="1.0" encoding="utf-8"?>
<packages>
  <package id="ServiceStack.Text" version="5.0.2" targetFramework="net45" />
  <package id="ServiceStack.Client" version="5.0.2" targetFramework="net45" />
  <package id="ServiceStack.Interfaces" version="5.0.2" targetFramework="net45" />
</packages>