Changes for Foreign Keys from 7.0.3 to 7.1beta?

Hello,
the following script is a simplified excerpt from a database for a
content-management-system:
--- snip ---
\connect template1 postgres
drop database test;
create database test;
\connect test postgres

create table LNG (
LNG_ID char(2),
LNG_NAME varchar(30),
primary key (LNG_ID)
)
;

create table OBJ (
OBJ_ID integer not null,
OBJ_LNG_ID char(2) constraint FK_OBJ_LNG_ID
references LNG(LNG_ID),
OBJ_CONT text,
primary key (OBJ_ID,OBJ_LNG_ID)
)
;

create table RSC (
RSC_ID serial,
RSC_OBJ_ID integer constraint FK_RSC_OBJ_ID
references OBJ(OBJ_ID)
on update cascade
on delete cascade,
primary key (RSC_ID)
)
;
--- snap ---

Resources for a page are collected in table RSC, language-dependancy is
resolved by combining OBJ_LNG_ID and OBJ_ID.
Now run in 7.0.3 (RedHat 7.0-RPMs) this script will do without problems,
however with 7.1beta (CVS updated on 12-28-2000) I get:
ERROR: UNIQUE constraint matching given keys for referenced table "obj" not
found
Do I have to have a UNIQUE index for OBJ_ID then? Well, I do not see the
point why this has to be.

Any hints?

Best Regards
Mirko