Foreign key validation failure in 18beta1

I've come across an unexpected ERROR during validation of FK constraint in PG
18beta1. The same works in PG 17:

drop table if exists fk;
drop table if exists pk;
create table pk(i int primary key) partition by range (i);
create table pk_1 partition of pk for values from (0) to (1);
create table pk_2 partition of pk for values from (1) to (2);
insert into pk values (0), (1);
create table fk(i int);
insert into fk values (1);

-- Works if the FK constraint is created as valid.
--alter table fk add foreign key(i) references pk;

-- Fails if the FK constraint is created as NOT VALID and validated
-- afterwards.
alter table fk add foreign key(i) references pk not valid;
alter table fk validate constraint fk_i_fkey;

--
Antonin Houska
Web: https://www.cybertec-postgresql.com