primefaces selectManyMenu required=true does not work

primefaces selectManyMenu required=true does not work

I have a form with several input fields (inputText, calendar,
selectManyMenu...). Some of them has the required attribute set to true
and it is working fine, but the selectManyMenu fields.
My code
<p:selectManyMenu id="channelsSelect"
value="#{bean.list}"
converter="dataConverter" showCheckbox="true" required="true"
requiredMessage="#{msg['field.required']}"
styleClass="manymenu">
<f:selectItems value="#{bean.completeList}" var="item"
itemValue="#{item}" itemLabel="#{item.name}" />
</p:selectManyMenu>
<p:message id="msgChannels" for="channelsSelect" />
And the requiredMessages is never shown even if I don´t select any value.
Thanks in advance. Regards.