[Moo] Fx.Tween Element.set() broken in 1.3?

[jdavidbakr]

Continuing my conversion from 1.2 to 1.3 I've discovered another
anomaly and am able to reproduce it with the following code.  In the
dom I just have a single absolutely positioned element with id of
"item."  On domready, I'm calling tween_1 which sets the options for
the element's tween to have the onComplete function as tween_2().
tween_2() pops an alert box and then resets the onComplete function to
a simple alert.

In 1.2, the DOM element slides to 500, alerts 'tween_1 complete',
slides to 100, and alerts 'tween 2 complete.'  In 1.3, the DOM element
slides to 500, alerts 'tween_1 complete', slides to 100, alerts
'tween_1 complete' then alerts 'tween_2 complete' and then gets stuck
in a loop.  It appears that when I'm calling $('item').set('tween') it
is appending the onComplete function instead of replacing it.  Is this
intended behavior or is it a bug?

  window.addEvent('domready',tween_1);
  function tween_1() {
    $('item').set('tween',{
      'onComplete':tween_2
    });
    $('item').tween('left',500);
  }
  function tween_2() {
    alert('tween_1 complete');
    $('item').set('tween',{
      'onComplete':function(){
         alert('tween 2 complete.');
      }
    });
    $('item').tween('left',100);
  }