JSF form value change does not work - jsf-2

Question

I have a form with 4 fields (2 dates, 2 selectOne).
My Bean is SessionScoped.
When I change the values in the form once, and click on submit, the applications works fine.
But when I want to change the values in form again, nothing happens. no change nor execution.
My Form looks like:
<ui:define name="sidebar">
<p:panel header="Select Values">
<h:form id="graphform">
<p:growl id="msg" />
<p:panelGrid columns="1">
<h:outputLabel for="servervalue" value="Servervalue: " />
<p:selectOneMenu value="#{graph.servervalue }" id="servervalue">
<f:selectItems value="#{formconst.SERVERVALUES}" />
</p:selectOneMenu>
<h:outputLabel for="startdate" value="Startdate: " />
<p:calendar disabledWeekends="false" size="10" pattern="dd.MM.yyyy"
showOtherMonths="true" maxlength="10"
mindate="#{formconst.MINDATE }" maxdate="#{formconst.MAXDATE}"
showButtonPanel="true" navigator="true" readOnlyInputText="true"
id="startdate" value="#{graph.startdate }" showOn="button"
required="true" />
<h:outputLabel for="enddate" value="Enddate: " />
<p:calendar disabledWeekends="false" size="10" pattern="dd.MM.yyyy"
showOtherMonths="true" maxlength="10"
mindate="#{formconst.MINDATE }" maxdate="#{formconst.MAXDATE }"
showButtonPanel="true" navigator="true" readOnlyInputText="true"
id="enddate" value="#{graph.enddate }" showOn="button"
required="true" />
<h:outputLabel for="filter" value="Filter: " />
<p:selectOneMenu value="#{graph.filter }" id="filter">
<f:selectItems value="#{formconst.GENERALFILTER}" />
</p:selectOneMenu>
</p:panelGrid>
<p:separator />
<p:panelGrid columns="2">
<p:commandButton value="Submit" update="#all"
action="#{ graph.updateChart }" />
<p:commandButton value="Reset" update="#all"
action="#{ graph.resetChart }" />
</p:panelGrid>
</h:form>
</p:panel>
</ui:define>
<ui:define name="content">
<h:form id="linechart">
<p:lineChart value="#{graph.cartesianChartBean.chartmodel }"
enhancedLegend="true" legendPosition="nw" xaxisAngle="50" />
</h:form>
</ui:define>
The same happens when I change SessionScoped to ViewScoped or RequestScoped.
I can change the values only one time.
I use primefaces 3.2 with apache myFaces 2.0.2 on WebSphere Application Server 8.0
Best Regards Veote