[TIMOB-10203] iOS: Map Annotation image cannot be changed dynamically

var changeButton = Ti.UI.createButton({
	title: 'change colour'
});
var win = Ti.UI.createWindow({
	rightNavButton: changeButton
});

var map = Ti.Map.createView({
	userLocation:false,
	animate: true,
	region: {
		latitude:12,
		longitude:12,
		latitudeDelta:1,
		longitudeDelta:1
	}
});

var annot = Ti.Map.createAnnotation({
	latitude:12,
	longitude:12,
	image: 'blue.png'
});

map.addAnnotation(annot);

win.add(map);
win.open({modal: true});

var isBlue = true;

changeButton.addEventListener('click', function(e){
	annot.image = isBlue ? 'yellow.png' : 'blue.png';
	isBlue = !isBlue;
});