Regrade Quiz Not working

[jellyfishvello]

Hi, I published a quiz and students have taken the quiz.

I want to regrade one of the questions such that all students have full credit.

I follow the guidance on the regrade page, by making a modification of the question, 

and then chose "give full credit for all students". but the regrade does not give full credits to all students.

Is this a bug of Canvas?