NOTIFY in multi-statement PQexec() not sent outside of transaction

macOS 10.13.6 (17G11023)
PostgreSQL 10.5 (Debian 10.5-2.pgdg90+1) on x86_64-pc-linux-gnu, compiled
by gcc (Debian 6.3.0-18+deb9u1) 6.3.0 20170516, 64-bit

Recreate with the following script. Expected behavior with TEST_DSN set to
your database. To see the broken behavior also set TEST_BREAK=1
---

# python 3.6
# set TEST_DSN env var

import os
import sys
import select
import psycopg2 # 2.8.4
from multiprocessing import Process, Queue

def notifier(input,output):
with psycopg2.connect(os.environ['TEST_DSN']) as conn:
conn.autocommit=True
with conn.cursor() as cur:
input.get()
if 'TEST_BREAK' in os.environ:
# docs seem to indicate that an implied transaction
# will not exist if there is an explicit begin/commit?
cur.execute(("notify __test; "
"begin; select pg_advisory_lock(7777); "
"select pg_advisory_unlock(7777); commit"))
else:
# this version works but introduces a race condition
# into my test suite where I am not sure that I am "in"
# a PQexec() but might instead be between such calls
cur.execute("notify __test")
cur.execute(( "select pg_advisory_lock(7777); "
"select pg_advisory_unlock(7777)"))
print('notifier unlocked', file=sys.stderr)
output.put(())

with psycopg2.connect(os.environ['TEST_DSN']) as conn:
conn.autocommit=True
with conn.cursor() as cur:
cur.execute("listen __test; select pg_advisory_lock(7777)")

input, output = Queue(), Queue()
p = Process(target=notifier, args=(output,input))
p.start()
output.put(())

print('waiting for notification',file=sys.stderr)
select.select([conn],[],[])
conn.poll()
print('notification received',file=sys.stderr)

cur.execute("select pg_advisory_unlock(7777)")

input.get()
p.join()