Dict copy optimization violates subclass invariant

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-02-17.22:12:32.940>
labels = ['type-bug']
title = 'Dict copy optimization violates subclass invariant'
updated_at = <Date 2021-02-19.02:54:18.442>
user = 'https://github.com/jab'

bugs.python.org fields:

activity = <Date 2021-02-19.02:54:18.442>
actor = 'methane'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2021-02-17.22:12:32.940>
creator = 'jab'
dependencies = []
files = []
hgrepos = []
issue_num = 43246
keywords = []
message_count = 4.0
messages = ['387191', '387198', '387206', '387279']
nosy_count = 6.0
nosy_names = ['rhettinger', 'jab', 'methane', 'serhiy.storchaka', 'josh.r', 'pgjones']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43246'
versions = []