on 8.0.1.FL.20151111 and later:
ListmodelList.setSelection, or addToSelection does not update the combobox main textbox.

This is likely related to following commit:
https://github.com/zkoss/zk/commit/59a6252be31615cdff192a3357249ccf1955cb61#diff-e1c31ce5bd0ed2c14db649d67bee47f7L114
on http://tracker.zkoss.org/browse/ZK-2937

See following example:
click on the button to select 1st Item.
Expected : item is selected and item value is set in the textbox.
Result : item is selected (in the model) but value is not set in the textbox.

<zk>
	<zscript><![CDATA[
		ListModelList myModel = new ListModelList();
		myModel.add("Value1");
		myModel.add("Value2");
		myModel.add("Value3");
		]]>
	</zscript>
    <combobox id="cmb" model="${myModel}"/>
    <button label="set selection on 1st item" onClick='cmb.model.clearSelection();cmb.model.addToSelection(cmb.model.get(0))'/>
</zk>

Additional data:

In combobox:setSelectedItem(Comboitem item) (called when model is updated)
setValueDirectly(item.getLabel()); set the value of the component, but does not trigger update on its own.
the smartUpdate("selectedItemUuid_", item.getUuid()); instruction cause the widget to correctly update its selected item property, but not its value.