This isn’t a bug, it’s a feature.
In memrise answers, commas indicate alternative answers. For example, if the answer in a course is given as “little, small” then you’re allowed to type either “little” or “small” as answers. You could also type “little, small” as an answer. In other words, you’re either allowed to give the entire string exactly, or you can give any of the comma-separated alternatives.
Obviously this doesn’t work quite so well for courses that have whole sentences or phrases with commas in them. But it works well enough. For example, if the correct answer is the phrase “those who hesitate, miss out”, you could just enter “those who hesitate” or “miss out” and have it marked correct - but if you’re actually trying to learn, you’re not going to do that. Seeing the prompt, if you know enough to know either the part before or after the comma, then you also know enough to know those aren’t really correct answers, so unless you’re trying to cheat your own learning by tricking memrise, you won’t just enter one part. You’ll try to give the whole answer, and if you don’t get the whole thing right, memrise will mark it wrong. So despite this quirk of memrise, no damage done.
However, there is one place where this quirk shows itself more forcefully, and that’s what you’ve encountered: Right after you get something incorrect during a review, memrise shows you the learning screen for it and prompts you to enter it again. This is not a quiz! Memrise shows you the correct answer, right there on the screen, and just has you type it in. This is re-learning practice.
Unlike normal learning, and unlike review quizzes, where you have to hit enter to submit your answer and get it checked, when you’re on this re-learning practice screen, you do not have to hit enter. As soon as you’ve typed a correct answer it is auto-submitted, instantly.
Of course, when the correct answer is a list of alternatives, you only have to type one of them, not the whole list. So as soon as you type one of them, it gets instantly auto-submitted. That’s okay for situations like “little, small”, where you type either “little” or “small” and it instantly turns green without waiting for you to hit enter. But with a phrase, it’s a bit jarring - it stops you after the first comma, because it thinks you have entered one of the alternative answers completely.
Overall, I think the comma-alternative syntax is extremely useful for course creators. I wish memrise would let course creators say, with a simple checkbox, whether a particular data column should or should not interpret commas as alternative answers; that way, a data column containing phrases could have that feature disabled. But for now, as long as memrise doesn’t have that feature, we’ll just have to live with that quirk on the re-learning screen after a wrong answer. Aside from that one place, where the harm is very limited, this feature does a lot more good than bad, and as long as you don’t deliberately take advantage of it to let yourself get things right when you know you don’t actually know them, it shouldn’t affect you noticeably.
