Why does the Synchronized method always return false?

In Windows Phone 8 (only on device!) try running this code:

public MainPage()
{
    InitializeComponent();

    var myTrue = GetTrue();
    Debug.WriteLine(myTrue);
    // false
}

[MethodImpl(MethodImplOptions.Synchronized)]
private static bool? GetTrue()
{
    return true;
}

You will see myTrue always is False! Why?! How it can be?!

UPDATE: Tested on devices: Nokia Lumia 920, HTC 8X, Nokia Lumia 925