MVVM: can't get clearSelection() to work properly with Listbox

<listbox model="@load(vm.tableDataModel)" selectedItems="@bind(vm.selectedTableItems)">
    ...
    <template name="model" var="tableItem">
        ...
    </template>
</listbox>

<button label="Dismiss" onClick="@command('dismissChanges')"></button>

private Set<ShiftBean> selectedTableItems = new HashSet<ShiftBean>();
private ListModelList<ShiftBean> tableDataModel = new ListModelList<ShiftBean>();

public Set<ShiftBean> getSelectedTableItems() {
        return selectedTableItems;
    }

public void setSelectedTableItems(final Set<ShiftBean> items) {
        selectedTableItems = items;
    }

public ListModelList<ShiftBean> getTableDataModel() {
        return tableDataModel;
    }

@Command
public void dismissChanges() {
    if (!selectedTableItems.isEmpty()) {
        tableDataModel.clearSelection();
    } else {
        Clients.showNotification("empty");
    }
}

@NotifyChange({"tableDataModel", "selectedTableItems"})