Problem with setting values in right column of TwinColSelect

I’m working on Liferay 6.0.6 and Vaadin 6.6.4.
I am trying to set values in right column of the component TwinColSelect.

I have a TwinColSelect containing employees with display property as name.

Relevant code is-

BeanItemContainer employeeContainer = new BeanItemContainer(
Employee.class, employeeList);

TwinColSelect twinColSelect = new TwinColSelect();

twinColSelect.setNullSelectionAllowed(true);
twinColSelect.setMultiSelect(true);
twinColSelect.setContainerDataSource(employeeContainer);
twinColSelect.setItemCaptionMode(TwinColSelect.ITEM_CAPTION_MODE_PROPERTY);
twinColSelect.setItemCaptionPropertyId(“name”);

twinColSelect.setLeftColumnCaption(“Available”);
twinColSelect.setRightColumnCaption(“Selected”);

I have a ListSelect called “employeeSelect” from which I get collection of employees. I convert this collection to a Set
and use this Set for setting default values in TwinColSelect. If I do a getValue() after the field has setValue() called,
the new value is returned. But this does not update the right column.

Code -

HashSet employeeSet = new HashSet();
Collection employeeCollection = (Collection) employeeSelect.getItemIds();
Iterator iterator = employeeCollection.iterator();
if(employeeCollection != null) {
if(!employeeCollection.isEmpty()) {
while (iterator.hasNext()) {
employeeSet.add(iterator.next());
}
}
}
productTwinColSelect.setValue(employeeSet);

What could be the possible problem here?