Right, we retired the four "challenge" badges (I believe they were arithmetic, pre-algebra, algebra, and trig) in favor of the new "topic" badges which replace

Right, we retired the four "challenge" badges (I believe they were arithmetic, pre-algebra, algebra, and trig) in favor of the new "topic" badges which replace what was there previously. I hadn't heard of anyone particularly upset about those badges, but we had many dozens of people who complained about the disappearance of the streak bar. We try our hardest not to hurt users' feelings but sometimes it's unavoidable as we make changes (hopefully for the better!).