Ajax re-rendering with Richfaces a4j

[ala alal]

I have a master detail that can be compiled many times with two buttons: one to save infos, and one to undo the operation and close the panel without save it.
With the commandLink "Insert new" I show the panel and the two buttons setting the variables rendoquadro=true and rendopulsanti=true.

<a4j:commandLink value="Insert new"  action="#{np_b.gestore_committenti.nuovo}" ajaxSingle="true" reRender="comm:quadro"/>

<rich:spacer height="12px" />

<f:subview id="comm">
 <a4j:outputPanel id="quadro">
  <rich:simpleTogglePanel switchType="client" rendered="#{np_b.first_committente.stato.rendoquadro}">
  <h:panelGrid columns="3" >
	<h:input id="denominazione" binding="#{np_b.first_committente.societa.denominazione}" required="true>
	</h:input>
	<h:input id="partitaiva" binding="#{np_b.first_committente.societa.partitaiva}" required="true">
	</h:input>
	<h:input id="codicefiscale"	binding="#{np_b.first_committente.societa.codicefiscale}" required="true">
	</h:input>
  </h:panelGrid>
  </rich:simpleTogglePanel>
 </a4j:outputPanel>
</f:subview>

<h:panelGrid columns="2">
 <a4j:commandButton  value="Undo"  reRender="committentilist,comm:quadro"
  action="#{np_b.gestore_committenti.annulla}" rendered="#{np_b.first_committente.stato.rendopulsanti}"
  immediate="true" type="submit">
 </a4j:commandButton>

 <a4j:commandButton value="Save" reRender="committentilist,comm:quadro"
  action="#{np_b.gestore_committenti.salva}" rendered="#{np_b.first_committente.stato.rendopulsanti}"
  type="submit">
 </a4j:commandButton>	
</h:panelGrid>

The problem is: if I press Insert New, compile some fields and then press Undo, the press Insert New again the input fields keep old inserted values when I want to be them blank. When I press Save or Undo the backing method called create a new Object and assign it to the variable np_b.first_committente.
With the Save button (without immediate attribute) everything is fine: if I press Insert New, compile fields, Save and then i click Insert New again all fields are blank; that not happens with undo, problably because of immediate attribute that is the only difference between the two buttons.
How can I solve it?

Thanks,

Alessandro.