Setting the X/Y positions initial values on Window doesn't propagate when the window is first initialized

[PureWeen]

Description

In our sandbox gallery use the following code

		protected override Window CreateWindow(IActivationState activationState) =>
			new Window(new NavigationPage( new MainPage()))
			{
				Width = 200,
				Height = 500,
				X = 0,
				Y = 500
			};

The width and height will propagate but the X/Y coordinates don't