如果属性访问,C#Struct方法不会保存值

下面的示例显示了问题.如果从Val属性执行结构test()方法,那么Val属性似乎会丢失该值,但如果该方法在Val2变量上执行,则该值似乎保持正确的值…

为什么会这样？

static class Program
{
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        new TestClass();
    }
}

public class TestClass
{
    public TestStruct Val { get; set; }
    private TestStruct Val2;

    public TestClass()
    {
        Val.test();
        Console.WriteLine(Val + "-> why is it not 10?");

        //Direct assignment works well...
        Val = 123;
        Console.WriteLine(Val  + "-> direct assingment works..");

        //This way works too. Why doesn't it work with "get;" and "set;"?
        Val2.test();
        Console.WriteLine(Val2 + "-> it works this way");
    }
}

public struct TestStruct
{
    private Int32 _Value;
    public long Offset { get; set; }

    public static implicit operator TestStruct(Int32 value)
    {
        return new TestStruct { _Value = value };
    }

    public static implicit operator Int32(TestStruct value)
    {
        return value._Value;
    }

    public void test()
    {
        _Value = 10;
    }
}