Under xp sp3 ie7, Can not scroll the mouse over the blank area.
Add an empty background-image to solve this problem.
This will produce an extra 'no-used' http connection(404)
But I have no better idead to solve it.
Under xp sp3 ie7, $el.outerHeight() or outerWidth() will retrive an
incorrect value.
This perhasp caused by the 'hasLayout' problem. Add 'zoom:1' to the
first child will solve the problem.