We recently encountered some IE9 incompatibility issues with our latest Moodle 2.1+ installation. It turns out that the used version of the graphical back-end Yui seems do have some problems with IE9 ,…. or the other way round :-).

There are couple of bug request in the moodle bug tracking system, but for 2.1+ there is unfortunately no commit in master which fixes this issue.

So if you do not want to wait for an official release take a look at -> link. Follow the walkthrough how to update Yui an this should fix the IE9 problems.

have fun