Approval Status field doesn't appear in custom DataFormWebPart

Question

I've got a very simple DataFormWebPart showing a single list item using XSLT.

I'd like to customize the display of the current Approval Status, but it doesn't render at all. The standard ListFormWebPart showed this field without issue, so there isn't a configuration issue with the List.

The column "Approval Status" is mapped to the attribute "@_ModerationStatus" and it is (by default) in the list of DataFields for the DataFormWebPart.

If I render out the Row's XML using the following technique, I notice that the _ModerationStatus field isn't in the result set.

<xmp><xsl:copy-of select="." /></xmp>

Is there something I need to do to configure the DataFormWebPart to make this field available?