Postgres: inserting single row, we got multiple

create table multi(id bigserial primary key, data text);
create table multi1(instance int2 not null default 1) inherits(multi);
create rule domultiply as on insert to multi do instead insert into multi1(data) values('auto1'), ('auto2') returning id, data;
insert into multi(data) values('manual') returning *; -- returns 2 rows!