pg_dump problem with dropped NOT NULL on child table

Please consider the following:

- Debian
- server is PG 9.4.5
- client (psql/pg_dump/libpq5) is 9.5

create table parent (
not_null_in_parent integer not null
);

create table child() inherits (parent);
alter table child
alter column not_null_in_parent
drop not null
;

Resulting in (as expected):

postgres(at)hermes:/tmp$ psql -d test
Ausgabeformat ist „wrapped“.
psql (9.5.0, Server 9.4.5)
Geben Sie „help“ für Hilfe ein.

test=# \d parent
Tabelle „public.parent“
Spalte | Typ | Attribute
--------------------+---------+-----------
not_null_in_parent | integer | not null
Anzahl Kindtabellen: 1 (Mit \d+ alle anzeigen.)

test=# \d child
Tabelle „public.child“
Spalte | Typ | Attribute
--------------------+---------+-----------
not_null_in_parent | integer |
Erbt von: parent

But getting dumped as (note the re-appearing NOT NULL
constraint on child):

--------------------------------------------------
--
-- PostgreSQL database dump
--

SET statement_timeout = 0;
SET lock_timeout = 0;
SET client_encoding = 'UTF8';
SET standard_conforming_strings = on;
SET check_function_bodies = false;
SET client_min_messages = warning;

--
-- Name: plpgsql; Type: EXTENSION; Schema: -; Owner:
--

CREATE EXTENSION IF NOT EXISTS plpgsql WITH SCHEMA pg_catalog;

--
-- Name: EXTENSION plpgsql; Type: COMMENT; Schema: -; Owner:
--

COMMENT ON EXTENSION plpgsql IS 'PL/pgSQL procedural language';

SET search_path = public, pg_catalog;

SET default_tablespace = '';

SET default_with_oids = false;

--
-- Name: parent; Type: TABLE; Schema: public; Owner: postgres; Tablespace:
--

CREATE TABLE parent (
not_null_in_parent integer NOT NULL
);

ALTER TABLE parent OWNER TO postgres;

--
-- Name: child; Type: TABLE; Schema: public; Owner: postgres; Tablespace:
--

CREATE TABLE child (
)
INHERITS (parent);

ALTER TABLE child OWNER TO postgres;

--
-- Data for Name: child; Type: TABLE DATA; Schema: public; Owner: postgres
--

COPY child (not_null_in_parent) FROM stdin;
\.

--
-- Data for Name: parent; Type: TABLE DATA; Schema: public; Owner: postgres
--

COPY parent (not_null_in_parent) FROM stdin;
\.

--
-- Name: public; Type: ACL; Schema: -; Owner: postgres
--

REVOKE ALL ON SCHEMA public FROM PUBLIC;
REVOKE ALL ON SCHEMA public FROM postgres;
GRANT ALL ON SCHEMA public TO postgres;
GRANT ALL ON SCHEMA public TO PUBLIC;

--
-- PostgreSQL database dump complete
--

--------------------------------------------------

Is this a bug or am I doing things I shouldn't hope work ?

I noticed this during a recent 9.4 -> 9.5 pg_upgradecluster
attempt with actual data in "child" violating-upon-restore
the newly created NOT NULL constraint on "child" when COPYing.

Thanks,
Karsten
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