Per this question I tried the following
<h:selectOneMenu id="branchSelect" value="#{cloner.branchType}">
<a4j:support event="onchange" ajaxSingle="true" rerender="branchSelect, branchPanel" />
<f:selectItem itemLabel="Constant" itemValue="constant" />
<f:selectItem itemLabel="Pattern" itemValue="pattern" />
</h:selectOneMenu>
<rich:togglePanel id="branchPanel" value="#{cloner.branchType}" switchType="ajax"
initialState="constant">
<f:facet name="constant">
<h:outputText value="Some block specific to Constant option" />
</f:facet>
<f:facet name="pattern">
<h:outputText value="Some block specific to Pattern option" />
</f:facet>
</rich:togglePanel>
Of course my backing bean has a setter/getter for branchType, and I can see that branchType is indeed being set when the select is changed. The toggle panel just isn't changing.