[SOLVED] primefaces p:dialog not rendering ui:include page component content

i have a p:dialog that looks like this:

<p:dialog ...>  
    <p:panel>
        <ui:include src="/webcomponents/presentation/user/testUserMenu.xhtml" />
    </p:panel>
</p:dialog>
(NOTE: "..." just means "etc/some code")

testUserMenu.xhtml looks like this:

...
<p:panelGrid id="testUserMenu">
...
    <p:commandButton value="#{msg['label.close']}" ... />
...
</p:panelGrid>
...

but the "close" button, nor anything else in the p:dialog, was getting rendered in the browser.
finally, i figured out (thanks to my colleague dan) that p:panelGrid simply needed a defined "columns" attribute, like this:

<p:panelGrid id="testUserMenu" columns="1">