// Prevent duplicate attachment of the collapsible behavior.
...

But this dont work. It realy does this twice.
Tested in IE7, Opera9.25, Opera9.5b, FF2.0.0.11, FF2.0.0.12... Both versions 0.8 and 1.X-dev... In two themes: my custom and garland:(

Firebug screenshot:
http://img215.imageshack.us/img215/8640/28947265ya9.png