Possible glitch in the interaction of a thread and a multiprocessing manager

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-01-04.19:19:03.378>
labels = ['interpreter-core', 'type-bug']
title = 'Possible glitch in the interaction of a thread and a multiprocessing manager'
updated_at = <Date 2021-06-19.01:01:58.106>
user = 'https://bugs.python.org/luke16'

bugs.python.org fields:

activity = <Date 2021-06-19.01:01:58.106>
actor = 'ethan.furman'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2017-01-04.19:19:03.378>
creator = 'luke_16'
dependencies = []
files = ['46145', '46159']
hgrepos = []
issue_num = 29158
keywords = []
message_count = 5.0
messages = ['284661', '284662', '284674', '284740', '284835']
nosy_count = 4.0
nosy_names = ['r.david.murray', 'ethan.furman', 'davin', 'luke_16']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue29158'
versions = ['Python 2.7', 'Python 3.6']