pgadmin2 1.4.12 edit record- update record

A select statement (on  serial_number=....) returns ONE record - in both ver 1.4.x and 1.2.x

CREATE TABLE inventorymaster (

warehouse_code char(3) NOT NULL,

serial_number varchar(16) NOT NULL,

class_code char(4) NOT NULL,

length int2 NOT NULL,

diameter int2 NOT NULL,

manufactured_date date NOT NULL,

sold_date char(10),

returned_date char(10),

customer_code char(6),

so_number numeric(10, 0),

inumcad numeric(10, 0),

bfm_unit_volume numeric(15, 2),

spothlf numeric(15, 2),

sale_currency char(3),

costrm numeric(15, 2),

costoh numeric(15, 2),

qty numeric(15, 2),

id int4 DEFAULT nextval('id'::text) NOT NULL,

spothwh numeric(15, 2),

spcadwh numeric(15, 2),

inumoth numeric(10, 0),

uom char(6),

bfm numeric(15, 5),

spcadlf numeric(15, 2),

CONSTRAINT inventoryindex UNIQUE (warehouse_code, serial_number, id),

CONSTRAINT inventory_key PRIMARY KEY (warehouse_code, serial_number, id),

CONSTRAINT "<unnamed>" FOREIGN KEY (warehouse_code) REFERENCES warehousemaster (warehouse_code) ON DELETE NO ACTION ON UPDATE NO ACTION NOT DEFERRABLE INITIALLY IMMEDIATE,

CONSTRAINT "<unnamed>" FOREIGN KEY (class_code) REFERENCES classmaster (class_code) ON DELETE NO ACTION ON UPDATE NO ACTION NOT DEFERRABLE INITIALLY IMMEDIATE

) WITH OIDS;