Orphaned namedspaced end tags such as </rich:panel> are not detected by the validation algorithm in contrast to orphaned namedspaced start tags:

<h:form id="searchForm">
<rich:panel>
<f:facet name="header">
<h:outputText value="ServiceProvider" />
</f:facet>

<a4j:commandButton value="Search" action="#

" />
</rich:panel>
</h:form>
</rich:panel>

The last end tag </rich:panel> above is orphaned but not detected as invalid by VPE.