Trouble understanding UI-Router and nested views

I'm setting up an AngularJS app using Angular UI Router using states.

In my app there are multiple pages, and two of them have a tabbed view. So I'm using nested views to display the pages that have tabs.

The problem is, when I navigate to a page with tabs, the back button does not appear in the header like it does when you navigate to a normal page.

I'm having trouble understanding why not. The tabbed view state might be abstract, but the first tab that is loaded isn't. So shouldn't the back button simply appear?

I've set up this Plunkr to demonstrate what I mean: