PrimeFaces selectOneMenu displayed value not resetting - primefaces

Question

I have two combo boxes. The items of the second one are retrieved using the selected value of the first one. When the default empty value is selected in the first combo box, the second combo box is not rendered.
Everything works well except for one scenario :
select a value in the first combo box -> the second combo box appears
select a value in the second combo box
select the default empty value in the first combo box -> the second combo box disappears
select the same value that was selected at step 1 in the first combo box
The second combo box should appear with the empty default value selected, but instead displays the value that was selected at step 2.
If I select a different value at step 4, the second combo box is loaded correctly, with the default empty value selected.
The view :
<ui:composition template="/pages/include/templatePrincipal.xhtml"
xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:p="http://primefaces.org/ui" xmlns:d="http://iec.composants"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:f="http://java.sun.com/jsf/core">
<ui:define name="pageActive">
<f:view>
<h:form>
<p:panel id="panelModifierUnParametreFonctionnel"
header="LISTE DES FE FILLES ORPHELINES">
<h:panelGrid columns="6">
<p:outputLabel
value="#{feFillesOrphelinesBean.labelComboRegion}" />
<p:selectOneMenu
value="#{feFillesOrphelinesBean.regionOption}"
valueChangeListener="#{feFillesOrphelinesBean.regionChanged}"
onchange="submit()">
<f:selectItems value="#{feFillesOrphelinesBean.listRegion}" />
</p:selectOneMenu>
<p:outputLabel
value="#{feFillesOrphelinesBean.labelComboCorps}"
rendered="#{feFillesOrphelinesBean.rendreComboCorps}" />
<p:selectOneMenu
value="#{feFillesOrphelinesBean.corpsOption}"
rendered="#{feFillesOrphelinesBean.rendreComboCorps}"
valueChangeListener="#{feFillesOrphelinesBean.corpsChanged}"
onchange="submit()">
<f:selectItems value="#{feFillesOrphelinesBean.listCorps}" />
</p:selectOneMenu>
</h:panelGrid>
</p:panel>
</h:form>
</f:view>
</ui:define>
</ui:composition>
The java bean :
public class FEFillesOrphelinesBean implements Serializable {
public final static String LABEL_COMBO_REGION = "Chaîne fonctionnelle :";
public final static String LABEL_COMBO_CORPS = "Corps :";
private String labelComboRegion;
private String labelComboCorps;
private List<SelectItem> listRegion;
private Integer regionOption;
private List<SelectItem> listCorps;
private Integer corpsOption;
private Boolean rendreComboCorps;
public String init() {
this.chargerRegions();
this.chargerCorps();
this.setLabelComboRegion(LABEL_COMBO_REGION);
this.setLabelComboCorps(LABEL_COMBO_CORPS);
return "success";
}
public void chargerRegions() {
this.setListRegion(new ArrayList<>());
this.setRegionOption(new Integer(-1));
RegionAdmin[] tabRegions = ServiceFactory.getInstance().getGestionRegionSrv().findAll();
this.getListRegion().add(new SelectItem(new Integer(-1), " "));
for (RegionAdmin region : tabRegions) {
SelectItem regionItem = new SelectItem(region.getId(), region.getLib() + ": " + region.getLibelle());
this.getListRegion().add(regionItem);
}
}
public void chargerCorps() {
this.setListCorps(new ArrayList<>());
this.setCorpsOption(new Integer(-1));
if (this.getRegionOption().equals(new Integer(-1))) {
this.setRendreComboCorps(false);
} else {
Corps[] tabCorps = ServiceFactory.getInstance().getGestionCorpsSrv().findCorps(this.getRegionOption());
this.getListCorps().add(new SelectItem(new Integer(-1), " "));
for (Corps corps : tabCorps) {
SelectItem corpsItem = new SelectItem(corps.getId(), corps.getLib() + ": " + corps.getLibelle());
this.getListCorps().add(corpsItem);
}
this.setRendreComboCorps(true);
}
}
public void regionChanged(ValueChangeEvent event) {
Integer newRegionOption = (Integer) event.getNewValue();
this.setRegionOption(newRegionOption);
this.chargerCorps();
}
public void corpsChanged(ValueChangeEvent event) {
Integer newCorpsOption = (Integer) event.getNewValue();
this.setCorpsOption(newCorpsOption);
}
public String getLabelComboRegion() {
return labelComboRegion;
}
public void setLabelComboRegion(String labelComboRegion) {
this.labelComboRegion = labelComboRegion;
}
public String getLabelComboCorps() {
return labelComboCorps;
}
public void setLabelComboCorps(String labelComboCorps) {
this.labelComboCorps = labelComboCorps;
}
public List<SelectItem> getListRegion() {
return listRegion;
}
public void setListRegion(List<SelectItem> listRegion) {
this.listRegion = listRegion;
}
public Integer getRegionOption() {
return regionOption;
}
public void setRegionOption(Integer regionOption) {
this.regionOption = regionOption;
}
public List<SelectItem> getListCorps() {
return listCorps;
}
public void setListCorps(List<SelectItem> listCorps) {
this.listCorps = listCorps;
}
public Integer getCorpsOption() {
return corpsOption;
}
public void setCorpsOption(Integer corpsOption) {
this.corpsOption = corpsOption;
}
public Boolean getRendreComboCorps() {
return rendreComboCorps;
}
public void setRendreComboCorps(Boolean rendreComboCorps) {
this.rendreComboCorps = rendreComboCorps;
}
}
As you can see, the regionChanged method is called when the selected value of the first combo box changes, then it calls the chargerCorps method which set the corpsOption to the -1 default value. This means that in the scenario that I've described, the displayed selected value is not the same as the selected value in the bean, which can cause a lot of issues.