I think I stumbled on a bug today; after submitting a question on shoddy Internet I was greeted with the "correct answer" sprites on the next unanswered question. Screenshots below:
Screenshot 2, this is on
Furthermore, clicking on the "Discuss sentence" button opens a modal which displays the correct answer to the question before you've answered it.
Yes, I have also noticed, If you start a lesson, disconnect the internet, you will get all problems right. and then on the last one Reconnect to the internet, and you will score 100%. I know a few people that take advantage of this, so maybe it's a good idea for Duolingo experts to look into this problem.