BUG #2123: join between stored procedures

The following bug has been logged online:

Bug reference: 2123
Logged by: Konstantin S. Zhinko [tIT]
Email address: k(dot)zhinko(at)grape(dot)ru
PostgreSQL version: 8.1.0
Operating system: CentOS 3.5
Description: join between stored procedures
Details:

Hi all!

I have a very big problem...

Here the code:

/*SQL START*/

CREATE TABLE "public"."test_data" (
"id" INTEGER NOT NULL,
"type" INTEGER NOT NULL,
"short_text" VARCHAR(255),
CONSTRAINT "test_data_pkey" PRIMARY KEY("id")
) WITH OIDS;

CREATE TYPE "public"."ret_id" AS (
"id" INTEGER
);

CREATE TYPE "public"."test" AS (
"id" INTEGER,
"type" INTEGER,
"info" VARCHAR(255)
);

CREATE OR REPLACE FUNCTION "public"."get_obj_list" () RETURNS SETOF
"public"."ret_id" AS
$body$
declare
ret ret_id;
begin

for ret in select test_data.id from test_data
loop

return next ret;

end loop;

end;
$body$
LANGUAGE 'plpgsql' VOLATILE CALLED ON NULL INPUT SECURITY INVOKER;

CREATE OR REPLACE FUNCTION "public"."get_obj" (id integer) RETURNS
"public"."test" AS
$body$
declare
ret test;
in_id alias for $1;

begin

select * from test_data a into ret where a.id=in_id;
return ret;

end;
$body$
LANGUAGE 'plpgsql' VOLATILE CALLED ON NULL INPUT SECURITY INVOKER;

/*SQL END*/

It is ok, but when I try to join these procedures, server responses error

/*SQL START*/
SELECT b.*
FROM get_obj_list a
LEFT JOIN get_obj(a.id) b ON 1=1
/*SQL END*/

Error: relation "a" does not exists.

Why it's so?