Tapping the button of the tab you're on doesn't always scroll to the top; it does always scroll to the default position. In the "All Photos" tab of the Photos a

Tapping the button of the tab you're on doesn't always scroll to the top; it does always scroll to the default position. In the "All Photos" tab of the Photos app, which is sorted with newest photos at the bottom, tapping the tab again will bring you down to the bottom, as that's the default position.