REFERENCES fails on derived classes

the following works:

create table t1 (id serial primary key);
create table t2 (id serial primary key);
create table t12 (
t1_id int references t1(id) on delete cascade,
t2_id int references t2(id) on delete cascade
);

but the following does not:
create table t1d () inherits(t1);
create table t1d2 (
t1d_id int references t1d(id) on delete cascade,
t2_id int references t2(id) on delete cascade
);

i'm told:
ERROR: UNIQUE constraint matching given keys for referenced table t1d not
found

i'm working in postgresql 7.1 (i686-pc-linux-gnu)

hope this is a bug (and i'm not wasting your time) and easily verifiable,
j. michael caine