"Back" vs. "return to collection"
Normally, a two finger pinch on an article returns the user to the browse page for the collection the article is in. Alternatively, the user can tap to reveal the title bar, and and the name of the collection is tappable in the upper-left corner of the screen.
However, if you have buttons that link between articles in a collection, and the user taps one of the buttons, the name of the collection in the title bar is replaced by "Back", so that the user can return to where they came from. But if you've followed several "jumps" this way by clicking on 4 buttons, for example, the user needs to tap "Back" 4 times before they can tap on the name of the collection to return to the browse page. Also, when a link is followed in this manner, the 2 finger pinch does nothing.
It is critical that a folio-type of experience still be possible in DPS 2015...and this can ALMOST be done simply by creating a collection with multiple articles. But this behavior really makes a collection consisting of linked articles very difficult to navigate.