I was attempting a question which was unrated and it had no solution, While I entered the first answer it came out to be incorrect, Then by mistake I clicked on 'no soultion' button the page where solution are shown was taken to, Though it did not had any solution still the correct answer was shown on the top, On the left hand side I clicked the back button and then as I still had attempts left I entered the answer and It said "CORRECT".
I found this strange and searched for another question which did not have any solution and repeated the process, I am adding the steps as I did
I entered a random answer, (Note that the problem has no solution yet it the question does not let me click on the No solution button,) and it came incorrect
When I entered one wrong answer it let me click on the No solution button
See that the correct option is written on the top.
I came back and entered the correct answer
And it says "CORRECT ANSWER"
This is what I found strange, This bug works for problem which has no solution yet, I will request someone to look into it.