Quiz with activity completion - "Or all available attempts completed" with unlimited attempts breaks the completion process

This bug is still present in 3.1. I originally tested on our institution's version 2.9.3.

While testing activity completion with badges, I came across a troublesome bug with Quiz:

In the Quiz settings, when you activate "Or all available attempts completed" but you also have an unlimited attempts allowed, the students never earn the related badge because, obviously, there is no attempts limit, but then it gets worst. Once the "Or all available attempts completed" is checked, it can no longer be disabled (even though it is presented as grayish, meaning that it is deactivated). So, the teacher gets stuck with an activity completion that doesn't work properly. I tried duplicating the Quiz, deleting the completion data (in the Course Administration) and playing around with different options but to no avail. The check mark still remains.

Thus, the only solution is to recreate the activity and make sure that I don't check the option again.

Steps to reproduce:

*Make sure that activity completion is activated in the course settings.

1. As a teacher or admin, create a Quiz activity
2. Set the Attempts limit to Unlimited
3. In the Activity completion section, check "Student must receive a grade to complete this activity", "Require passing grade" and "Or all available attempts completed".
4. Save.
5. Go back to the Quiz settings and uncheck the "Require passing grade" and "Or all available attempts completed".
6. Save.
7. Go back again in the settings... the "Or all available attempts completed" is still checked, but it is grayish (supposed to be deactivated).
8. As a student, complete the Quiz attempt.
   Result: no matter how many times you attempt the Quiz, it will never be completed because the "Or all available attempts completed" is stuck in the settings.

I hope the description is clear for everyone, if not, don't hesitate to ask me some questions.