I am using an iPhone 6 Plus and the mobile app. When I am on the first screen of a thread (before scrolling down) and I decide to exit the thread, I press "Active" in the top left corner and it takes me back to the Active Threads. If on the other hand I stay in a thread and decide to scroll further down and then want to leave, I get a different result. In this instance, pressing "Active" simply takes me to the top of the thread. This is odd behaviour as the word "Active" at the top of the screen should be no more than a simple link with no complex logic behind it and yet it is acting more like a "back" button on a PC - i.e. taking me back to where I have just come from - which may be the Active thread list or simply the screen of posts above the screen I'm currently on.
Either way, it's an issue for the techies in the New Year.