Some student submissions made to the assignment activity are invisible to the instructors (1.9.5 and 1.9.8)
Student uploads a file or posts online text in the Assignment activity. Student can see his own submission just fine there.
Instructors do not. But they can see the rest of the submissions in the same activity.
Instructor can re-sort the assignment submissions page by any other column, e.g. by Last Modified. This will magically reveal the "missing" submission.
I have marked it as major, because instructors assume that such student missed the assignment, and give that student a bad grade.
We found out that the cause of the bug is multiple entries into the database. (e.g. student managed to click on Upload button multiple times)
We have tried to reproduce the bug, but we were not able to. It seems that certain conditions need to be just right for the bug to happen. It might be server lagging, or pushing the submit button at a specific interval.
Querying the database found 67 duplicate entries by users from 200,000 entries in the assignment_submissions table that have been submitted in total. So, it seems to be a very rare bug. However, it does happen
- http://moodle.org/mod/forum/discuss.php?d=157789&parent=711385 (report of the same issue)