jQuery use addEventListener/attachEvent to add event handler.

when use addEventListener, the event object will pass in handler's first argument.

attachEvent is the same as addEventListener when get the event object in IE6/7/8.

So, in the method jQuery.event.dispatch, the first line

event = jQuery.event.fix( event || window.event );

should modify as

event = jQuery.event.fix( event );

see testcase in IE6/7/8: http://jsfiddle.net/aLaD3/1/