Another gotcha to look out for, which you somewhat discovered here. The YUI2 in pre-2.3.x Moodle worked in various browsers. YUI3 conflicts with the interpretation of mouse vs touch vs tablet vs 'smart board' inputs. Newest IE on Windows, Safari, latest Chromium, seem to work, FF and Chrome fail. AJAX on Moodle stops working correctly.
Trouble tickets have been posted in several places, including with the YUI development team.