From the forum post: http://moodle.org/mod/forum/discuss.php?d=82928

"In Moodle 1.8.2 a weird phenomenon with the viewing of grades. The course in question has mostly Forums some of which have had posts rated. The teacher of the course reported that she couldn't view the grades in the gradebook, but when I log in as administrator I can view the grades fine. Doing a 'login as' to the teacher's account confirms the disappearance of the individual grades (see attached screenshot). Fiddling about with Preferences, weights etc has no effect. Now, when I return to the Administrator account I get the same behaviour – no grades are visible. Logging out and back in again resets everything. This problem is repeatable but I've only seen it in this particular class."

and my report:

"We are running moodle 1.8.2 on a Win2k3 server. Every other class that is using the gradebook has no problem. In this particular class the teacher has a blank gradebook. As admin I can see the grades until I login as her and then revert back to my account.

At that point I can no longer see any grades until I logout and log back in.

I've set her gradebook prefs/settings to match that of a working class gradebook, unhidden all hidden items, and made sure grouping is turned off. Nothing has worked so far. The only thing that appears different about her account is that she is in the Orphan group, as I imported her from a previous install.

Thinking that the orphan status may have some impact, I elevated a test user to the status of teacher within the course. The test user is able to see grades when I use the "login as," option."

A screenshot of the gradebook is attached.