The response from a GET_FEATURES request sent to an ArcMap Service may contain fields not specified in the SPATIALQUERY element's subfields attribute.
ArcMap Server will respond differently depending on the data source of the map layer being queried.
For personal geodatabase and geodatabase layers the #SHAPE# field will always be returned along with any fields specified in the request's subfields attribute.
For all other data sources all fields will be returned, no matter what fields are specified in the request's subfields attribute (This is not an issue in ArcIMS 9.0. Subfield in GET_FEATURES request will be honored.)