DataColumn with Expression is null in xsd designer

[michael.neel]

I have a simple datatable created in the vwd xsd designer, and have
added one additional column that has an expression set to the
difference of two columns (col1 - col2). Using "Preview" on the select
methods, the expression column works fine. When an object data source
is set to the datatable, the expression column always returns null (or
the default). Is there an additional property or method that needs to
be called for a object data source or gridview to run the expression
stored in the datacolumn?