When an Event is triggered by a user in IE, it is set to the window.event object. The only way to see what triggered the event is by accessing the window.
window.event
window.
I solved the issue with a patch:
window.ValidatorHookupEvent = function(control, eventType, body) { $(control).bind(eventType.slice(2), new Function("event", body)); };
Update: I've submitted the issue to MS (link).