I was trying to add my email address as a cc in bug 13440 but I can't seem to be able to. This is the error I was getting: Only the owner or submitter of the bug, or a sufficiently empowered user, may make that change to the rep_platform field. Old value: New value: All So it appears that when the bug was entered, the Platform was set to blank. However, the dropdown for Platform on the bug screen doesn't have a "blank" option, and I don't have permission to set the value to All.
These are most likely browswer/database errors and cannot be fixed in bugzilla. The best thing you could do is contact me if you encounter a bug like this, and I can fix it for you.