Steps to Reproduce

<zk>
  <zscript><![CDATA[
    ListModel model = new ListModelList(Locale.getAvailableLocales());
    model.setMultiple(true);
    model.addToSelection(Locale.ENGLISH);

    ListModel subModel = ListModels.toListSubModel(model);
    ]]>
  </zscript>
  <searchbox model="${subModel}" />
</zk>

1. Open the searchbox, search for en

Current Result

en is not selected

Expected Result

en is selected

Debug Information

selectedUuids:[null]

If ListModel is a SubModel, full items won't be passed to client. Thus no item will be generated with a proper UUID.
Since _itemUuidRelations is empty. The result will be always null.

Workaround

1. Use a ListModel (not a ListSubModel)
2. Don't select any item at first