Buttons for toggles have this inherent problem: should they show state, or should they show action? Twitter elevated it to the whole new level: in one state it shows state, in another it shows action. To top that off, after a few years teaching users their visual clues they completely inverted the visual code.
If only somebody invented a control that can unabmigiously show the state and the action...
Left to right: Twitter before/Twiter after/My proposal