[TIMOB-24825] Windows: Ti.UI.View.center is incorrectly calculated

var window = Ti.UI.createWindow({backgroundColor: 'gray'}),
    a = Ti.UI.createView({backgroundColor: 'red', width: 200, height: 200, top: 0, left: 0}),
    b = Ti.UI.createView({backgroundColor: 'blue', width: 100, height: 100, center: {x: 150, y: 150}}),
    btn_a = Ti.UI.createButton({title: 'TOP LEFT', bottom: 0, left: 0, width: '50%'}),
    btn_b = Ti.UI.createButton({title: 'ZERO', bottom: 0, right: 0, width: '50%'});

btn_a.addEventListener('click', function(){
    b.center = {x: '50%', y: '50%'};
});

window.add([btn_a, a, b]);
window.open();