[Seaside] annoying POST when loading prototype

[Sebastian Sastre]

Hi guys,
I've porting an app to seaside 2.9a2 and when starting to make it work I've
found an annoying POST happening just at the end of the load of the page.
That POST was not caused by any user action. It just happens on load or
something. I was messing around investigating (it also happens with seaside
2.8.3) until (don't ask me why) I've disable loading prototype in the
updateRoot:

So, if I load prototype (prototype-1.6.0.3.js) I have that sh*ty POST which
creates a new sesion and N troubles, but if I don't  load it, then is all is
just fine.

It has to be prototype because I've tested loading only jQuery and all is just
fine.

it is a known issue? any ideas/solution?
thanks,

sebastian