It seems that h:selectManyListbox does not work on rich:modalPanel, using richfaces 3.2.2.BETA5.
The component does not pass selected values. (A list of String in my case).
It works though in 3.2.1 GA.

<rich:modalPanel id="addPropertyModalPanel" height="700" width="600">
 <f:facet name="header">#{messages['addDictionary.addProperty']}</f:facet>
 <a4j:form id="formo">
 <rich:panel id="commonPrpertiesPanel" style="border: 0px;">
 <h:outputLabel value="#{messages['addDictionary.visibilityLevel']}: " />
 <h:selectManyListbox id="newPropertyVisibilityLevel" value="#{addDictionaryBean.authorities}" size="3">
 <c:forEach var="item" items="#{addDictionaryBean.availableAuthorities}">
 <f:selectItem itemValue="#{item}" />
 </c:forEach>
 </h:selectManyListbox>
 <h:message for="newPropertyVisibilityLevel" />
 </rich:panel>
 <rich:panel style="border: 0px;">
 <h:panelGrid id="buttonPanel" columns="2">
 <a4j:commandButton id="closeModalButton" value="#{ messages['close'] }" immediate="true" />
 <a4j:commandButton id="addPropertyButton" value="#{ messages['save'] }" action="#{addDictionaryBean.addProperty}"
 type="submit" reRender="lista" />
 </h:panelGrid>
 </rich:panel>
 <rich:componentControl id="controller" for="addPropertyModalPanel" attachTo="closeModalButton" operation="hide"
 event="onclick" />
 </a4j:form>
 </rich:modalPanel>