Crossword - Keep correct answers on retry ?

Hello fellow users !

I need help to figure out what purpose serves the following setting in the Crossword content-type : "Keep correct answers on retry ?" (If this option is enabled, correct answers will be kept when the user retries the task). 

In my mind, it means that when a user hits the "Check" button after having done his crossword, if he has entered some correct words, then, when he hits the "Retry" button, his crossword is not completely reset : the correct words are kept on the grid ; only the wrong ones are cleared.

But, that's not what happens : if I activate this setting, the entire crossword is cleared when I hit the "retry" button, even the correct answers. As a matter of fact, I see no difference if I uncheck the box. I can't grasp the intended effect. So, if anyone can clear things out for me, I'd be grateful.

Thanks in advance :)

Isabelle