The Append and Delete buttons are disabled when XPServerCollectionSource is used

I'm following example E1729 using the DynamicDataTableClassInfo and want to use the new DataNavigator. I can edit cells and when I set the NewItemRowPosition to Bottom I can add new records. But the buttons + and - are never enabled. Please assist.

XAML
<mygrid:DevGrid x:Name="grid" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">  
    <dxg:GridControl.View>  
        <dxg:TableView Name="gridview" AllowFixedGroups="True" ShowTotalSummary="False" ShowAutoFilterRow="True" BestFitMode="Smart" MultiSelectMode="Row" NewItemRowPosition="Bottom"  ShowDataNavigator="True" >  
        </dxg:TableView>  
    </dxg:GridControl.View>  
</mygrid:DevGrid>  

C#
XpoDefault.DataLayer = XpoDefault.GetDataLayer(Database.XpoConnectionString, DevExpress.Xpo.DB.AutoCreateOption.None);  
var workSession = new Session();  
DbConnection conn = Database.CreateConnection() as DbConnection;  
DbDataAdapter adapter = Database.createDataAdapter() as DbDataAdapter;  
DbCommand selectCommand = conn.CreateCommand();  
selectCommand.CommandText = "select * from " + Database.encloseTableName(tableName);  
adapter.SelectCommand = selectCommand;  
DataTable dataTable = new DataTable(tableName);  
adapter.FillSchema(dataTable, SchemaType.Source);  

XPServerCollectionSource dataSource = new XPServerCollectionSource(workSession, new DynamicDataTableClassInfo(workSession.Dictionary, dataTable));  
dataSource.AllowEdit = true;  
dataSource.AllowNew = true;  
dataSource.AllowRemove = true;  

grid.ItemsSource = dataSource;  
grid.PopulateColumns();  

gridview.AllowEditing = true;