Invalid value when debugging in Visual Studio 2015

Let's assume we have some sample code (VS2015, WinForms, .Net 4.6.1):

List<int> items = new List<int>();
private async Task test(int id)
{
    id = 1;
    int id_real = id;

    int index = items.FindIndex(x => x == id);
}

private async void button1_Click(object sender, EventArgs e)
{
    await test(0);
}

      

        
        
        
      

    

Now the "function":

How is this possible? The interesting part is this is just a Visual Studio observer issue, the execution result remains correct.

So far I know this only happens in VS2015 and the reason for this behavior is the last line in the test method.