From the mail "State saving of UIViewParameter" on jsr-314-open:
UIViewParameter uses the submittedValue to store its value in the state for the
next postback, because obviously the view parameter won't be in the request
parameter map of the next request (which is the postback). But because its
submittedValue is null after the conversions and validations, it has to be set
again before the state is generated. To accomplish that, the spec currently
states to override encodeAll() and make the call to setSubmittedValue() there.
In addition, encodeAll() has to be called in UIViewRoot.encodeEnd() for every
UIViewParameter in the view. This works perfectly for normal requests, but when
you are using an AJAX request the state is generated before
UIViewRoot.encodeEnd() is called an thus the submittedValue for every
UIViewParameter is null in the state. This means that the value of every
UIViewParameter will be null in the following request.
Now the easiest solution to this problem, which I also already committed to
MyFaces trunk (again see  for details), is to do mostly the same as in
UIViewRoot.encodeEnd() just also in PartialViewContext.
processPartial() when the PhaseId is RENDER_RESPONSE before the state is
generated to make it work for AJAX-requests.
However I don't really like this solution, because we have to think of handling
UIViewParameters in a special way every time we change something on any render
mechanism. Why don't we just override saveState() on UIViewParameter and set the
submittedValue there before the state is saved. This will have the same result,
but without the code in UIViewRoot, PartialViewContext and
UIViewParameter.encodeAll() and without future headaches. I also already
uploaded a patch for this to the MyFaces issue at .
Answer to this from Martin Marinschek: "This is just a so much better solution
. We should spec this one."