<zk>
You should see the outline border is fitted to the listbox's height, if not that is a bug.
	<div vflex="min">
	<listbox rows="20" hflex="min">
			<zscript><![CDATA[
				List list = new ArrayList();
				for (int i = 0; i < 20; i++)
					list.add("item " + i);
			]]></zscript>
			<listitem forEach="${list}">
				<listcell label="${each}"/>
				<listcell label="${each}"/>
			</listitem>
		</listbox>
	</div>
</zk>