Composite type operator not unique

Hi,
I'm trying to make a custom composite type and use it as a PK and FK.
When adding FK to table I've got trhis error: operator is not unique:
"BigintRef" pg_catalog.= "BigintRef" (see below). Here is my type
definition with operator:

CREATE TYPE "BigintRef" AS
   ("Value" bigint,
    "Null" boolean);

CREATE OR REPLACE FUNCTION bigintref_op_eq("BigintRef", "BigintRef")
  RETURNS boolean AS
'SELECT ($1."Null" = TRUE AND $2."Null" = TRUE) OR ($1."Null" = FALSe
AND $2."Null" = FALSE AND $1."Value" = $2."Value")'
  LANGUAGE sql IMMUTABLE
  COST 100;

CREATE OPERATOR =(
  PROCEDURE = bigintref_op_eq,
  LEFTARG = "BigintRef",
  RIGHTARG = "BigintRef");

Here are table definitions:

CREATE TEMP TABLE t_a(id "BigintRef");
CREATE TEMP TABLE t_b(id "BigintRef");
ALTER TABLE t_a ADD PRIMARY KEY(id);

NOTICE:  ALTER TABLE / ADD PRIMARY KEY will create implicit index
"t_a_pkey" for table "t_a"
Query returned successfully with no result in 51 ms.

ALTER TABLE t_b ADD FOREIGN KEY(id) REFERENCES t_a(id);

ERROR:  operator is not unique: "BigintRef" pg_catalog.= "BigintRef"
LINE 1: ..._temp_6"."t_a" pk ON ( pk."id"::pg_catalog.record
OPERATOR(p...
                                                             ^
HINT:  Could not choose a best candidate operator. You might need to
add explicit type casts.
QUERY:  SELECT fk."id" FROM ONLY "pg_temp_6"."t_b" fk LEFT OUTER JOIN
ONLY "pg_temp_6"."t_a" pk ON ( pk."id"::pg_catalog.record
OPERATOR(pg_catalog.=) fk."id"::pg_catalog.record) WHERE pk."id" IS
NULL AND (fk."id" IS NOT NULL)

Anyone know what is wrong? I'm using PostgreSQL 9.0

Thanks

Trigve