@converter causes a big performance issue on the nested children binding

<zk xmlns:x="xhtml">
	<zscript><![CDATA[
	public class MyVM {
		public void setChildren(List children) {}
		public List getChildren() {
			int size = 100;
			List s = new ArrayList(size);
			for (int i = 0; i < size; i++)
				s.add(i);
			return s;
		}
		public void setConcatConverter(Converter c) {}
		public Converter getConcatConverter() { return new ConcatConverter();}
		class ConcatConverter implements Converter {
		    public Object coerceToUi(Object val, Component comp, BindContext ctx) {
		    	return "";
		    }
		    public Object coerceToBean(Object val, Component comp, BindContext ctx) {
		    	return null;
		    }
		}
	}
	]]></zscript>
	<div id="bind" apply="org.zkoss.bind.BindComposer"
		viewModel="@id('vm') @init('MyVM')">
		<x:table id="host" border="1" children="@load(vm.children)">
			<template name="children" var="r">
				<x:tr children="@load(vm.children)">
					<template name="children" var="gb">
						<x:td>
							<label
								style='@load(vm.children) @converter(vm.concatConverter,x=r,y=gb,z=gb, format="background:rgb(%s,%s,%s)")' />
						</x:td>
					</template>
				</x:tr>
			</template>
		</x:table>
	</div>
</zk>