// this function determines whether the event is the equivalent of the microsoft // mouseleave or mouseenter events. 
function isMouseLeaveOrEnter(e, handler) { 
  if (e.type != 'mouseout' && e.type != 'mouseover') return false; 
  var reltg = e.relatedTarget ? e.relatedTarget : 
  e.type == 'mouseout' ? e.toElement : e.fromElement; 
  while (reltg && reltg != handler) reltg = reltg.parentNode; 
  return (reltg != handler); 
}

http://www.dynamic-tools.net/toolbox/isMouseLeaveOrEnter/

So the event is fired only once when hovering over child elements

IsMouseLeaveOrEnter - Fix for mouseover/mouseout

JavaScript