Answers contains punctuation marks only cannot be answered correctly, even if I use the on screen keyboard. It shouldn’t be the problem of the course because I find this problem in more than one course.
Can you please post a screenshot?
Ah, now I think I understand more 
Are you a contributor to this course, and can you please post a link to this course?
This issue exists in more than one course, and I am not a contributor to any of these courses.
For example:
https://www.memrise.com/course/171188/learn-basic-english-braille/ (I made the screenshots from this one)
https://www.memrise.com/course/437713/myanmar-burmese-alphabetscript/ (the vowel part and the punctuation part)
https://www.memrise.com/course/151/learn-morse-code/ (Level 5 contains tapping tests which cannot be passed and I give up learning. I haven’t checked the levels after level 5 yet but it might be the same.)
A week has passed. Nothing happens.
Ya, sorry :\ I’m not on the Memrise team, so there’s not a lot I can do.
The problem is still not solved. Pushing.
I’ve found this same issue in lesson 13 this Afrikaans course on both the Android app and the mobile website (Opera browser). Even the hints are counted as wrong.
I’ve got screenshots if they are needed.
Rather than making a new topic, I hope it’s fine to just bump this one. It’s a frustrating problem!
I encountered the exact same issue taking this Hebrew typing course. I am using Memrise on Web, through Opera browser.