I have a ZUL page looking similar to:
<zk xmlns="http://www.zkoss.org/2005/zul" xmlns:h="http://www.w3.org/1999/xhtml">
[...]
<h:table style="position:absolute;right:2px;bottom:2px;">
<h:tr>
<h:td><button id="refreshButton" /></h:td>
[...]

and I try to query the button:
desktopAgent.query("#refreshButton") it always returns null.