ERROR: domain domain1 does not allow null values

Hello.
I've found unexpected behavior of PostgreSQL 8.2.3

CREATE DOMAIN "public"."domain1" AS integer NOT NULL;

CREATE TABLE "public"."table1" ("field1" "public"."domain1") WITH OIDS;

CREATE OR REPLACE FUNCTION "public"."function1" () RETURNS text AS
$body$
declare
a public.table1%ROWTYPE;
begin
return 'test';
end;
$body$
LANGUAGE 'plpgsql' VOLATILE CALLED ON NULL INPUT SECURITY INVOKER;

Result:
ERROR: domain domain1 does not allow null values
CONTEXT: PL/pgSQL function "function1" line 3 at block variables
initialization

I think it is insane.
Any comments wellcome...