Summary: Regrading on a test after changing one score messes up grades
Moodle version: 1.8
I constructed a multiple choice quizz, with just one question and 20 possible answers, with more than one possible answer correct. Each correct (wrong) answer scored 10% (-10%) of the grade, for a total of 10. Option "mix answers within question" was checked.
As the quizz was closing, I noticed one ambiguous answer and decided to change that score from -10% to 10%. I also added/changed some of the feedbacks. The program warned me that the maximum possible score was now 110% (which was okay for me since the maximum real score was 4/10 anyway) but allowed me to proceed. By then it was either one minute before or after closing time.
After I hit the "regrade" the button, all grades changed randomly. (I could remember most of them and they were changing by more than 2/10). Upon close inspection, and with the help of a "before" and "after" printout which I happened to have, I realized the answers had been scrambled up (in different order) but not the checked boxes ! Hence the random grades. The printout clearly shows it is the same attempt (same number), same order of checked boxes, but different order of answers.
All students emailed me to let me know that the answers now marked as theirs were not their answers.
I tried changing the closing date to after the current date (seemed to work for similar problems for other people in the forum) and it got worse.
Now most of the grades were 10 (max grade used to be 4).
I changed the score back to what it used to be and now got reasonable looking scores (i.e., 0 to 2) but still different from before.
To complicate matters, I am also pretty sure that grading was not working before I did the changes to the score, the night before the big mess. I was looking at one of the tests, whose score was 0 when my eyes were telling me it should have been 2 (she had 4 answers correct, 2 wrong ones). Another one which should have been a 0 had a 2/10. So I hit "regrade" and the scores appeared to fix themselves.
But in retrospect I can't tel whether they really got fixed or whether it was a random arrangement like the one I experienced the next day.
I can reproduce the random grading by changing the scoring once again.
I am attaching the quizz.