Steps to Reproduce

Run fiddle:
http://zkfiddle.org/sample/pg2al7/2-itemiter-returns-footer

Current Result

Listbox throw a
"org.zkoss.zul.Listfoot cannot be cast to org.zkoss.zul.Listitem"
exception during org.zkoss.zul.Listbox.renderItems(Set<? extends Listitem>)
because it expects only listitems and received a listfooter instead

Expected Result

Client shouldn't send non-listitems to be rendered

Debug Info

set of items to render (which shouldn't contain Listfooter but does in this case) is sent to server by
zul.mesh.MeshWidget.prototype._onRender

During _onRender, the list of listitems is built using zul.sel.ItemIter which should only return listitems
However, the ItemIter init will skip visible(false) children of listbox until it finds a child that is not visible(false).
Since this is done using nextSibling, init will return any child, not just listitems

Root Cause

ItemIter init doesn't filter non-item children of mesh widget

Workaround

<script><![CDATA[
	zk.afterLoad('zul.sel', function() {
		var xItemIter = {};
		zk.override(zul.sel.ItemIter.prototype, xItemIter ,{
			_init: function () {
				if (!this._isInit) {
					this._isInit = true;
					var p = this.box.firstItem;
					if (this.opts && this.opts.skipHidden)
						for (; p && !p.isVisible(); p = p.parent.nextItem(p)) {}
					this.p = p;
				}
			}
		});//zk.override
	});//zk.afterLoad
	]]></script>