referential integrity problem

It seems we can create a forein key using REFERENCES privilege but
cannot drop the table if its owner is not same as the referenced
table. Is this a feature or bug?

-- create a table as user foo
\c - foo
create table t1(i int primary key);
-- grant reference privilege to user bar
grant references on t1 to bar;
-- create a table as user bar
\c - bar
create table t2(i int references t1);
-- cannot drop t2 as user bar?
drop table t2;
NOTICE:  DROP TABLE implicitly drops referential integrity trigger from table "t1"
ERROR:  t1: Must be table owner.
--
Tatsuo Ishii