TableHeaderScope enum does not generate XHTML-compliant output

When adding the scope attribute to a column for accessibility, the following does not generate XHTML-compliant output:

TableHeaderCell th = new TableHeaderCell();
th.Scope = TableHeaderScope.Column;

It generates the following HTML:

<th scope="column">

The value of the scope attribute should be "col". A work-around is to add the scope attribute manually using the Attributes collection:

th.Attributes.Add("scope", "col");