BUG #10822: "ALTER SYSTEM cannot run inside a transaction block" when having autocommit disabled.

The following bug has been logged on the website:

Bug reference: 10822
Logged by: Feike Steenbergen
Email address: feikesteenbergen(at)gmail(dot)com
PostgreSQL version: 9.4beta1
Operating system: Debian 3.2.57-3+deb7u2 i686 GNU/Linux
Description:

When having AUTOCOMMIT disabled, issuing an ALTER SYSTEM reports an error.
Enabling AUTOCOMMIT makes the issue disappear.

$ psql feike feikesuper -h localhost -p 5433 --no-psqlrc
psql (9.4beta1)
SSL connection (protocol: TLSv1.2, cipher: ECDHE-RSA-AES256-GCM-SHA384,
bits: 256)
Type "help" for help.

feike=# \set AUTOCOMMIT off
feike=# rollback;
WARNING: there is no transaction in progress
ROLLBACK
feike=# ALTER SYSTEM SET log_min_duration_statement = '5s';
ERROR: ALTER SYSTEM cannot run inside a transaction block
feike=# rollback;
ROLLBACK
feike=# \set AUTOCOMMIT on
feike=# ALTER SYSTEM SET log_min_duration_statement = '5s';
ALTER SYSTEM

The documentation states:

"This command is not allowed inside transaction block or function."

in my understanding, i am not *yet* inside a transaction block when issuing
the ALTER SYSTEM, so I assume it would work when having AUTOCOMMIT enabled,
but then after a comleted transaction.

To me the current behaviour is odd, as VACUUM, which also mentions "VACUUM
cannot be executed inside a transaction block." is able to be executed when
having AUTOCOMMIT disabled:

$ psql feike feikesuper -h localhost -p 5433 --no-psqlrc
psql (9.4beta1)
SSL connection (protocol: TLSv1.2, cipher: ECDHE-RSA-AES256-GCM-SHA384,
bits: 256)
Type "help" for help.

feike=# \set AUTOCOMMIT off
feike=# SELECT 1;
?column?
----------
1
(1 row)

feike=# VACUUM;
ERROR: VACUUM cannot run inside a transaction block
feike=# rollback;
ROLLBACK
feike=# \set AUTOCOMMIT on
feike=# VACUUM;
VACUUM