Value of two selectOneMenu will not set, just for one in the middle for Model.

<s:div style="margin-top:5px">
 <h:form>

 <s:validateAll>

 <rich:panel>
 <h:panelGroup id="frms">
 <h:panelGrid columns="2">
 <h:outputText value="FNr: "/> <h:outputText value="#{kfz.id}"/>
 </h:panelGrid>
 <h:panelGrid columns="3">
 <h:outputText value="Fabrikat: "/>
 <h:panelGroup style="display:block">
 <a4j:region renderRegionOnly="false">
 <h:selectOneMenu id="hrs" value="#{kfz.hersteller}" required="true" converter="#{bearbkfz.herconverter}">
 <s:selectItems value="#{herstellersList}" var="her" label="#{her.bezeichnung}" noSelectionLabel="Bitte waehlen..." />
 <a4j:support event="onchange"
 reRender="modelsel" />
 </h:selectOneMenu>
 </a4j:region>
 </h:panelGroup>
 <h:message for="hrs" />

 <h:outputText value="Modell:" />
 <h:panelGroup style="display:block" id="modelsel" >
 <a4j:region renderRegionOnly="false">
 <h:selectOneMenu value="#{kfz.kfzmodel}" required="true" converter="#{bearbkfz.modconverter1}">
 <s:selectItems value="#{kfz.hersteller.kfzmodel}" var="md" label="#{md.bezeichnung}" noSelectionLabel="Bitte waehlen..." />
 </h:selectOneMenu>
 </a4j:region>
 </h:panelGroup>
 <h:message for="modelsel" />

 <h:outputText value="Filiale:" />
 <h:selectOneMenu id="fillsel" value="#{kfz.filliale}" required="true" converter="#{fillconverter}">
 <s:selectItems value="#{fillList}" var="md" label="#{md.bezeichnung}" noSelectionLabel="Bitte waehlen..." />
 </h:selectOneMenu>
 <h:message for="fillsel" />

 </h:panelGrid>
 </h:panelGroup>