Pressing backspace in a "ticking-the-right-answer" question
It often happens to me and my family (my whole familiy uses Duolingo). If you tick the wrong answer and you press backspace as a reflex of deleting, you go back one site so everything you have done in the lesson is resetted. Please fix it, sometimes it is really nerve-wracking.
(Please excuse my terrible english, I hope you get the point :))