Problem about ViewController get isLast() after setRoot()

There are two pages, login and tabs. The first page is login page, after sign-in, I used NavController to setRoot(TabsPage). Then I checked the tabs page is the last page by ViewController.isLast(). I expected the result is true, but I got false. Is that correct?
I also printed the stack of views in tabs page. I got 2 views in array, but there is only one view after I expanded the array to look detail.