UIInstructions cannot be cast to AbstractTogglePanelItem

Hoje me aconteceu o seguinte erro num projeto com jsf2 e richfaces4:

com.sun.faces.facelets.compiler.UIInstructions cannot be cast to org.richfaces.component.AbstractTogglePanelItem

No meu caso descobri que o que causava isso eram comentários dentro do tabPanel.

NÃO FUNCIONA:
<rich:tabPanel>
<rich:tab header="aaaaa">
<h:outputText value="aaaaaaaaaa"></h:outputText>
</rich:tab>
<!— esse comentario gerou o erro -->
<rich:tab header="bbbbb">
<h:outputText value="bbbbbbbbbb"></h:outputText>
</rich:tab>
</rich:tabPanel>

FUNCIONA:
<rich:tabPanel>
<rich:tab header="aaaaa">
<h:outputText value="aaaaaaaaaa"></h:outputText>
</rich:tab>
<rich:tab header="bbbbb">
<h:outputText value="bbbbbbbbbb"></h:outputText>
</rich:tab>
</rich:tabPanel>


Log com mais detalhes:
10:36:35,449 SEVERE [javax.enterprise.resource.webcontainer.jsf.application] Error Rendering View[/resources/user/UserForm.xhtml]: java.lang.ClassCastException: com.sun.faces.facelets.compiler.UIInstructions cannot be cast to org.richfaces.component.AbstractTogglePanelItem
at org.richfaces.renderkit.html.TogglePanelRenderer.getChildrenScriptObjects(TogglePanelRenderer.java:178) [:4.0.0-SNAPSHOT]

[…]
10:36:35,493 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[localhost].[/l8-web].[Faces Servlet]] Servlet.service() for servlet Faces Servlet threw exception: java.lang.ClassCastException: com.sun.faces.facelets.compiler.UIInstructions cannot be cast to org.richfaces.component.AbstractTogglePanelItem
at org.richfaces.renderkit.html.TogglePanelRenderer.getChildrenScriptObjects(TogglePanelRenderer.java:178) [:4.0.0-SNAPSHOT]
at org.richfaces.renderkit.html.TogglePanelRenderer.getScriptObjectOptions(TogglePanelRenderer.java:147) [:4.0.0-SNAPSHOT]

[…]