Comment 2 for bug 1187850

Yes by that we meant not to have a back button and tabs on the same screen. I have updated the description here : http://design.ubuntu.com/apps/global-patterns/navigation

When we need to use deep navigation, for example when the user taps on a piece of content from a tabbed view, the header will update to represent the new view.

The page stack (deep navigation) introduces a back button which, when combined with tabs (flat navigation) in the same view, could be misinterpreted as another method for navigating between tabs.