In converting my site from 1.8 to 1.9, I found that the results reported by the gradebook for a particular course (and possibly more than that course, but it's the one I noticed) changed during the upgrade. Essentially what happened was the overall course grades of two students, which were 68.58% and 65.23% in Moodle 1.8 (a calculation that was in fact correct, as verified by me on a calculator), were changed to 64.49% and 64.69% respectively (meaning that the students also changed rank order within the class). An important thing to note is that the grades themselves all stayed the same and are still recorded correctly in the 1.9 Moodle; it is, as far as I can tell, a calculation error of some kind that was introduced by the upgrading of the grading categories (or something to that effect). This is, needless to say, disturbing, as our instructors (including myself) expect to be able to go back and look at accurate historical grade information.

I have attached a 1.8 backup of the course whittled down to its bare essentials: the assignments and grading categories, and two anonymized users with the grades in question. Importing it into a 1.8 Moodle gives the correct result percentages; importing it into a 1.9 Moodle gives incorrect results (though, oddly, different incorrect results than were obtained by upgrading from 1.8 to 1.9). I have not tried again performing the upgrade process on the course after importing it into a 1.8 Moodle, but my assumption is that it will give the same incorrect results that I see in my current upgraded Moodle.