grid column doesn't reappear if columns menupopup set to auto and grid is sizedByContent

<zk>
	<grid sizedByContent="true">
		<columns menupopup="auto">
			<column label="Author" sort="auto" />
			<column label="Title" sort="auto" />
			<column label="Publisher" sort="auto" />
			<column label="Hardcover" sort="auto" />
		</columns>
		<rows>
			<row>
				<label value="Philip Hensher" />
				<label value="The Northern Clemency" />
				<label value="Knopf (October 30, 2008)" />
				<label value="608 pages" />
			</row>
			<row>
				<label value="Philip Hensher" />
				<label value="The Fit" />
				<label value="HarperPerennial (April 4, 2005)" />
				<label value="240 pages" />
			</row>
		</rows>
	</grid>
</zk>