We're on Moodle 2.8. In a course that has been reset (with students deleted/assignments/grades deleted) we have a student re-taking the course. When we enrolled student in the reset course, all of his grades came back with him. I manually cleared out grades, but in the assignment modules, the old grades are still showing, and the only option is to override in the grader report; which invalidates weighting/totals.
We had the same issue last semester, but we were able to work around because the course used a very simple natural grading method (only 7 grades in the whole course), and the student had previously dropped after the first two assignments, so we did an override on those two, and the rest were accepted as is. Since it was an isolated incident I just assumed the instructor had failed to check a box in the reset.