onOpen event listener didn't trigger when using GroupsModel

<zk>
	<zscript><![CDATA[
List head = new ArrayList();
List data = new ArrayList();
head.add("group1");
head.add("group2");
data.add(new ArrayList());
data.add(new ArrayList());
SimpleGroupsModel groupmodel = new SimpleGroupsModel(data, head);
for (int i = 0, len = groupmodel.getGroupCount(); i < len; i++) {
	groupmodel.removeOpenGroup(i);
}
	]]></zscript>
	<grid model="${groupmodel}">
		<columns>
			<column label="Col" />
		</columns>
		<template name="model:group">
			<group label="${each}" onOpen='Clients.showNotification("Open Group")' />
		</template>
		<template name="model">
			<row>
				<label value="${each}" />
			</row>
		</template>
	</grid>
</zk>