BUG #11524: Unable to add value to ENUM when having AUTOCOMMIT disabled in psql

The following bug has been logged on the website:

Bug reference: 11524
Logged by: Feike Steenbergen
Email address: feikesteenbergen(at)gmail(dot)com
PostgreSQL version: 9.4beta2
Operating system: Debian
Description:

If I want to add a value to an ENUM type, I cannot do so when having
AUTOCOMMIT enabled.

To reproduce:
\set ECHO queries
CREATE TYPE mood AS ENUM ('sad', 'ok', 'happy');
ALTER TYPE mood ADD VALUE 'autocommit enabled';
\set AUTOCOMMIT OFF
ALTER TYPE mood ADD VALUE 'autocommit disabled';

Output:
CREATE TYPE mood AS ENUM ('sad', 'ok', 'happy');
CREATE TYPE
ALTER TYPE mood ADD VALUE 'autocommit enabled';
ALTER TYPE
ALTER TYPE mood ADD VALUE 'autocommit disabled';
psql:autocommit_enum.sql:5: ERROR: ALTER TYPE ... ADD cannot run inside a
transaction block

I have this issue on 9.1 - 9.5. (This issue does not occur on 9.0 as adding
"ADD VALUE" was added in 9.1).

This bug reminds me of:
BUG #10822: "ALTER SYSTEM cannot run inside a transaction block" when having
autocommit disabled.