BUG #15042: Parition by list using enums odd behaviour

The following bug has been logged on the website:

Bug reference: 15042
Logged by: Damir Ciganović-Janković
Email address: damir(dot)ciganovic(dot)jankovic(at)gmail(dot)com
PostgreSQL version: 10.1
Operating system: Windows 10
Description:

First time asking question, if you like stackoverflow, check this link
https://stackoverflow.com/questions/48502345/postgresql-10-partition-by-list-using-enums?noredirect=1#comment84079025_48502345

If not, I will explain. I am trying to partition my table using enum as
partition condition, this is what I did:

create type positivity as enum (
'POSITIVE',
'NEGATIVE'
);

create table test (id int, polarity positivity) partition by list
(polarity);
create table test_1 partition of test for values in ('POSITIVE');
create table test_2 partition of test for values in ('NEGATIVE');

####

explain select * from test where polarity = 'NEGATIVE';
(output:)
explain select * from test where polarity = 'NEGATIVE';
QUERY PLAN
--------------------------------------------------------------
Append (cost=0.00..76.50 rows=22 width=8)
-> Seq Scan on test_1 (cost=0.00..38.25 rows=11 width=8)
Filter: (polarity = 'NEGATIVE'::positivity)
-> Seq Scan on test_2 (cost=0.00..38.25 rows=11 width=8)
Filter: (polarity = 'NEGATIVE'::positivity)
(5 rows)

####
I expected that it will only scan test_2, adding constraints on both
partitions will get me desired behaviour:

alter table test_1 add constraint test_1_check check(polarity='POSITIVE');
alter table test_2 add constraint test_2_check check(polarity='NEGATIVE');

explain select * from test where polarity = 'NEGATIVE';
(output:)
QUERY PLAN
--------------------------------------------------------------
Append (cost=0.00..38.25 rows=11 width=8)
-> Seq Scan on test_2 (cost=0.00..38.25 rows=11 width=8)
Filter: (polarity = 'NEGATIVE'::positivity)
(3 rows)

###

Is this a bug or is it not implemented yet maybe? Or is it working as
intended?
Thank you in advance