[gnome-db] Invalid GdaDataModelIter

what can cause an invalid GdaDataModelIter?

i have some tables, where a simple "SELECT * FROM <tablename>" returns  
an invalid iter after gda_data_model_iter_move_next; on other tables  
of the same db it works

i'm using libgda 4.2.10 from git HEAD, with postgresql 8.3.14, under  
windows (under gnu/linux with postgresql 9.1 it works)

2 examples

CREATE TABLE atti
(
   id integer NOT NULL,
   numero character varying(10) DEFAULT ''::character varying,
   data date,
   anno integer DEFAULT 0,
   protocollo character varying(50) DEFAULT ''::character varying,
   data_protocollo date,
   gen_intervento character varying(255) DEFAULT ''::character varying,
   note character varying(255) DEFAULT ''::character varying,
   abitabilita integer DEFAULT 0,
   n_piani integer DEFAULT 0,
   n_appartamenti integer DEFAULT 0,
   pi_sottosuolo real DEFAULT 0,
   vani_utili real DEFAULT 0,
   accessori real DEFAULT 0,
   altri_vani real DEFAULT 0,
   tot_vani real DEFAULT 0,
   volumetria real DEFAULT 0,
   rec_collegato integer DEFAULT 0,
   visibile boolean DEFAULT false,
   id_tipi_atto integer DEFAULT 0,
   id_efficacia integer DEFAULT 0,
   pr_cod_prat_civilia integer DEFAULT 0,
   id_edifici integer DEFAULT 0,
   CONSTRAINT atti_pkey PRIMARY KEY (id )
)

CREATE TABLE atti_vie
(
   id_atti integer NOT NULL,
   id_vie integer NOT NULL,
   civico character varying(50) NOT NULL DEFAULT ''::character varying,
   CONSTRAINT atti_vie_pkey PRIMARY KEY (id_atti , id_vie , civico )
)

CREATE TABLE visure
(
   id integer NOT NULL,
   data timestamp without time zone,
   id_modalita_richiesta integer DEFAULT 0,
   id_richiedenti integer DEFAULT 0,
   id_qualita_di integer DEFAULT 0,
   protocollo character varying(20) DEFAULT ''::character varying,
   note text DEFAULT ''::text,
   data_conferma_richiesta timestamp without time zone,
   note_conferma_richiesta text DEFAULT ''::text,
   tipo_conferma_richiesta integer DEFAULT 0, -- 1 - confermata...
   status character varying(1) DEFAULT ''::character varying,
   CONSTRAINT visure_pkey PRIMARY KEY (id )
)

CREATE TABLE visura_atti
(
   id integer NOT NULL,
   id_visure integer,
   id_atti integer,
   numero character varying(10) DEFAULT ''::character varying,
   id_tipi_atto integer,
   data date,
   protocollo character varying(50) DEFAULT ''::character varying,
   data_protocollo date,
   intestatari character varying(255) DEFAULT ''::character varying,
   indirizzi character varying(255) DEFAULT ''::character varying,
   note text DEFAULT ''::text,
   status character varying(1) DEFAULT ''::character varying,
   tipo_conferma_richiesta integer DEFAULT 0, -- 1 - confermata...
   data_conferma_richiesta timestamp without time zone,
   note_conferma_richiesta text,
   tipo_esito_ricerca integer DEFAULT 0, -- 1 - pronto...
   data_esito_ricerca timestamp without time zone,
   note_esito_ricerca text DEFAULT ''::text,
   data_da_consegnare timestamp without time zone,
   note_da_consegnare text DEFAULT ''::text,
   data_consegna timestamp without time zone,
   note_consegna text DEFAULT ''::text,
   data_ritiro timestamp without time zone,
   note_ritiro text DEFAULT ''::text,
   data_da_ritirare timestamp without time zone,
   note_da_ritirare text DEFAULT ''::text,
   data_invio_email timestamp without time zone,
   CONSTRAINT visura_atti_pkey PRIMARY KEY (id )
)

with "atti" it returns invalid, but with "atti_vie" it works

with "visure" it works, but with "visura_atti" it returns invalid

thanks in advance