Created Unassigned: UpdatePanelAnimationExtender onUpdating never fired [27993]

Hi,

I'm trying to use UpdatePanelAnimationExtender for a FadeIn/FadeOut effect but OnUpdating event is not fired.
I have to use Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(BeginRequestHandler) in order to get it working.

Could you please tell me what am I doing wrong?

sample project:
https://dl.dropboxusercontent.com/u/5073388/Test.zip

Thank you,
Josep