selection setter does not work (ScollableDataTable)

[lschreiber]

Hello

the example code below show how i use the scollabledatatable
i use the SimpleSelection to take the Selection from the DataTable but when i click on the ajax button the setter (setSelection) does not work.
Only the takeSelection Method was called.

can anyone help me?

 <rich:panel style="padding:0" headerClass="outpanelHeader">
 <f:facet name="header">
 <h:outputText value="Vorgänge" id="paramnemsd" />
 </f:facet>
 <rich:dropSupport id="dne1t" acceptedTypes="GOBPERSON" dropValue="GOBPERSON"
 dropListener="#{backing_gobpersonsearch.processDrop}" reRender="gopselection,planneddateearch">
 </rich:dropSupport>

 <h:panelGrid columns="1" align="center">
 <rich:scrollableDataTable rowKeyVar="rkv" frozenColCount="1" height="100px"
 width="700px" id="planneddateearch" rows="40" columnClasses="col" selection="#{backing_gobpersonsearch.selection}"
 value="#{backing_gobpersonsearch.searchedPlannedDates}" var="gpd">
 <rich:column id="p2d_id" >
 <f:facet name="header"><h:outputText styleClass="headerText" value="ID" /></f:facet>
 <h:outputText value="#{gpd.p2d_id}" id="a1"/>
 </rich:column>
 <rich:column id="act_name">
 <f:facet name="header"><h:outputText styleClass="headerText" value="Action" /></f:facet>
 <h:outputText value="#{gpd.act_name}" id="a2"/>
 </rich:column>
 <rich:column id="status">
 <f:facet name="header"><h:outputText styleClass="headerText" value="status" /></f:facet>
 <h:outputText value="#{gpd.status}" id="a3"/>
 </rich:column>
 <rich:column id="planned_date">
 <f:facet name="header"><h:outputText styleClass="headerText" value="Soll Datum" /></f:facet>
 <h:outputText value="#{gpd.planned_date}" id="a4"/>
 </rich:column>
 <rich:column id="next_call_date">
 <f:facet name="header"><h:outputText styleClass="headerText" value="Ist Datum" /></f:facet>
 <h:outputText value="#{gpd.next_call_date}" id="a5"/>
 </rich:column>
 </rich:scrollableDataTable>
 <a4j:commandButton value="Show Current Selection" action="#{backing_gobpersonsearch.takeSelection}"/>
 </h:panelGrid>
 </rich:panel>

here is the JavaCode for setter and getter of Selection and the method takeSelection

 public SimpleSelection getSelection() {
 return selection;
 }

 public void setSelection(SimpleSelection selection) {
 System.out.println("im in Selectionsetter");
 this.selection = selection;
 }


 public String takeSelection() {
 System.out.println("im here in takeSelection");
 System.out.println(getSelection().size());
 getSelectedPlannedDate().clear();
 Iterator<SimpleRowKey> iterator = getSelection().getKeys();

 while (iterator.hasNext()){
 System.out.println("Selection found");
 SimpleRowKey key = iterator.next();
 }
 System.out.println(getSelectedPlannedDate().size());
 return null;
 }