Thanks for your reply. I will try to answer your questions, but I also have a question myself. The question is: Why would you want to loose grades when a student unenrols en re-enrols into a course? To me that makes no sense at all.
The answer to your questions are:
1. We have an instance of the previous system still available, but I don't see how this solves our problems. We are not going to let our students work in 2 Moodles, one old and one new.
2. ' why are you not able to restore your grades en masse through a query updating the mdl_grade_grades with the most recent corresponding entry from mdl_grade_grades_history?'
Please tell me how...
3. If you mean we shouldn't be using open source unless we now how to fix programming flaws, than I disagree with you. In simple terms: we signed up for Moodle because it is good and cheap - and that fits the budget in these times. If we had more money perhaps we would choose differntly or be able to hire programmers, but we are a school and not an IT company.
Furthermore, we do spend money for hosting and upgrading our Moodle by a Moodlepartner. But if there's flaws in the Moodle code, we turn to both our Moodle partner and the community.
I hope I've answered your questions.