ToJson() extension method serialization order with ServiceStack

gistfile1.cs

    public class LogMessage
    {
        // This property moved to be overriden in derived classes
        protected string _time = DateTime.UtcNow.ToString("dd/MM/yyyy HH:mm:ss.fff");

        public LogLevel Level { get; protected set; }
    }

    public class InfoLogMessage : LogMessage
    {
        public InfoLogMessage()
        {
            Level = LogLevel.Info;
        }

        // This property is moved out from base class 
        // to make sure it's order to be first in the serialized Json
        public string Time { get { return _time; } }

        public object Message { get; set; }
        public List<string> Tags { get; set; }

        public override string ToString()
        {
            return this.ToJson();
        }
    }