BUG #13675: Problem statement “INSERT ON CONFLICT WHERE"

The following bug has been logged on the website:

Bug reference: 13675
Logged by: nmgjinan
Email address: nmgjinan(at)126(dot)com
PostgreSQL version: 9.5beta1
Operating system: CentOS release 5.6 32bit
Description:

Hi,I'm testing pg9.5 beta1, encounter a problem, detailed description:

postgres=# create table distributors(did int primary key,dname
varchar,is_active boolean);
CREATE TABLE
postgres=# insert into distributors values(1,'hyl',false),(2,'aaa',true);
INSERT 0 2
postgres=# select * from distributors ;
did | dname | is_active
-----+-------+-----------
1 | hyl | f
2 | aaa | t
(2 rows)

postgres=# insert into distributors values (2,'bbb')
postgres-# on conflict (did) where is_active do update set
dname=EXCLUDED.dname;
INSERT 0 1
postgres=# select * from distributors ;
did | dname | is_active
-----+-------+-----------
1 | hyl | f
2 | bbb | t
(2 rows)

postgres=# insert into distributors values (1,'hgdb')
postgres-# on conflict (did) where is_active do update set
dname=EXCLUDED.dname;
INSERT 0 1
postgres=# select * from distributors ;
did | dname | is_active
-----+-------+-----------
2 | bbb | t
1 | hgdb | f
(2 rows)

postgres=#

Why, when the where condition is true or false, the fields are change?