futures cancelled by ThreadPoolExecutor.shutdown() not yielded by as_completed()

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-04-04.11:59:46.446>
labels = ['type-bug', 'library', '3.9']
title = 'futures cancelled by ThreadPoolExecutor.shutdown() not yielded by as_completed()'
updated_at = <Date 2021-04-04.11:59:46.446>
user = 'https://github.com/bigbenhur'

bugs.python.org fields:

activity = <Date 2021-04-04.11:59:46.446>
actor = 'bigbenhur'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-04-04.11:59:46.446>
creator = 'bigbenhur'
dependencies = []
files = []
hgrepos = []
issue_num = 43727
keywords = []
message_count = 1.0
messages = ['390183']
nosy_count = 1.0
nosy_names = ['bigbenhur']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43727'
versions = ['Python 3.9']