Moo 1.2 offsetHeight pb in Creative Pony's sliding tabs

[ghazal]

Hi,
I have ported almost successfully Creative Pony's sliding tabs to 1.2
(not very difficult, good code to begin with)
Original demo here : http://creativepony.com/demos/sliding-tabs/
my 1.2 version here : http://ghazalp.co.cc/sliding_tabs/sliding-tabs8.html

I have a remaining pb with height resizing, according to content
height.

In properties, it is thus defined:
var SlidingTabs = new Class({
***
animateHeight: true, // animate height of container
***
heightFx: null, // this one animates the height

then ...
  if (this.options.animateHeight)
      this.heightFx.set(this.panes[this.current].offsetHeight);

***
  if (this.options.animateHeight)
      this.heightFx.get(this.panes[this.current].offsetHeight);

where I put a (lame) get(this.panes[this.current].offsetHeight);

instead of the original
 start(this.panes[this.current].offsetHeight);

not finding any other way to make it work.

Any help ?