It looks like there is a bug in
PageNavigator. I'll get that fixed in the next update.
Until then, as a workaround, you can set
selectedIndex after the
PageNavigator has validated for the first time.
var navigator = new PageNavigator();
navigator.dataProvider = new ArrayCollection([PageItem.withClass(Page1), PageItem.withClass(Page2), PageItem.withClass(Page3)]);
navigator.selectedIndex = 2;