We just upgraded from Moodle 2.0.10 to 2.3.4. Everything works fine in Chrome and Firefox, but not in Internet Explorer (9 and 10 at least). All the problems I have encountered seem to be different manifestations of the same thing.
1. In IE 10, the overview report page does not update upon selecting a student from the drop-down list.
2. A similar problem occurs when using the Assignment Upgrade Helper.
3. In some roles, the Marking block appears first, taking up the whole width of the browser window, instead of in its place with the other blocks.
4. Markers can't attach response files, because the file picker never loads. They get stuck on this screen: