Can't edit rows

In one of our Postgresql databases pgadmin (1.8.4) shows a strange
behaviour: I can't edit row data in some of the tables.

All tables have primary keys, but no OIDS. All tables have the same
owner and belong to the same database and schema. This problem only
occurs in pgadmin, in any other postgresql database editor I have tried
, editing works fine.

An example:

CAN NOT edit data:
---------------

CREATE TABLE knve_property_multilang_field
(
id serial NOT NULL,
id_language integer NOT NULL,
id_property integer NOT NULL,
"name" character varying(250) NOT NULL,
value_txt text,
CONSTRAINT knve_property_multilang_field_pkey PRIMARY KEY (id),
CONSTRAINT fk_knve_property_multilang_field_language FOREIGN KEY
(id_language)
REFERENCES knve_language (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE RESTRICT,
CONSTRAINT fk_knve_property_multilang_field_property FOREIGN KEY
(id_property)
REFERENCES knve_property (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE CASCADE
)
WITH (OIDS=FALSE);

CAN edit data:
-------------

CREATE TABLE knve_instance
(
id serial NOT NULL,
id_type integer NOT NULL,
deleted boolean NOT NULL DEFAULT false,
created_on timestamp without time zone NOT NULL DEFAULT now(),
changed_on timestamp without time zone,
created_by integer,
changed_by integer,
CONSTRAINT knve_instance_pkey PRIMARY KEY (id),
CONSTRAINT fk_knve_instance_type FOREIGN KEY (id_type)
REFERENCES knve_type (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE RESTRICT
)
WITH (OIDS=FALSE);

Any ideas on that would be very appreciated.

Thanks in advance,
Roman