Set a model to combobox when opening, the dropdown will not show the items

<zk>
<zscript><![CDATA[
String[] dictionary =

{ "abacus", "abase", "barcarole", "barefaced", "cadence", "cadenza", "death's-head", "debacle", "endear", "endemic", "endue", "facial", "facile", "facilitate", "gaiety", "gaily", "gainsay", "writhe", "writing", "wry", }

;

ListModel dictModel= new SimpleListModel(dictionary);
]]></zscript>
<div>
1. type 'a', the dropdownlist shall show 2 items.
</div>
<combobox autodrop="true" >
<attribute name="onOpen"><![CDATA[
self.setModel(dictModel);
]]></attribute>
</combobox>
</zk>