Index: lib/instance_methods.rb
===================================================================
--- lib/instance_methods.rb	(.../vendor/acts_as_solr/0.7)	(revision 494)
+++ lib/instance_methods.rb	(.../trunk/sw/ObsidianPortal/vendor/plugins/acts_as_solr)	(revision 494)
@@ -47,7 +47,13 @@
           field_type = get_solr_field_type(field.values[0])
         end
         value = self.send("#{field_name}_for_solr")
-        doc.add_element field("#{field_name}_#{field_type}", value.to_s) unless field.to_s == "id"
+        
+        # add the field to the document, but only if it's not the id field
+        # or the type field (from single table inheritance), since these
+        # fields have already been added above.
+        if (field.to_s != "id") and (field.to_s != "type")
+          doc.add_element field("#{field_name}_#{field_type}", value.to_s)
+        end
       end
       
       add_includes(doc) unless configuration[:include].nil?