Firebird return wrong value

Dear List!

i have a strange problem.

I have a Firebird database (dialect 3). Firebird server: 2.0.6
I create a table, and insert a row like that:
CREATE TABLE PRICE (
  ID INTEGER NOT NULL,
  "NAME" VARCHAR(10),
  COST NUMERIC(15, 2));

INSERT INTO PRICE (ID, "NAME", COST)
VALUES (2, 'my price2', -1);

when i read it back i get strange value. I get -0.0 and not -1.

            $db=new PDO("firebird:dbname=localhost:c:/test/test.fdb","testuser","testpassword",array());
            $sql="select cost from price where id=2";
            $q=$db->query($sql);
            $ret=$q->fetchAll(PDO::FETCH_ASSOC);
            print_r($ret);

result:
Array ( [0] => Array ( [COST] => -0.00 ) )

Thanks for your advice,
Berko