I don't remember exactly how it started, but I was doing a lesson in German, and all of a sudden this strange glitch started happening that was carried throughout the entire lesson. I experimented with it and this is what I gathered:
No matter what, it reads the first action you do. If you have to translate a sentence, it will deem it correct or incorrect upon the first letter you type, and this is dependent on whether or not you got the previous question marked correct.
You can click on the discussion of the sentence before having attempted the question.
When the lesson is "green," the only way to get a question wrong is to get a question that asks you to write out the sentence in the language you're learning based on a speaker. When the glitch is active, however, the speaker is broken. The speaker icon doesn't even appear. If you type a single letter, it automatically marks it wrong, but you can still type.
If you start typing on a translation question while Duolingo is green, the entire textbox will turn green asif you are correct and will let you hit the "continue" button. If you're wrong, though, it still says you're correct, but it doesn't add a green progress bar at the top. However, it still gives you the progress (I finished the lesson and it still said I have four questions left).
Has a similar thing happened to anyone else? Sorry, I didn't get any screenshots...