MagicMock specialisation instance can no longer be passed to new MagicMock instance

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-02-07.09:38:41.606>
labels = ['3.8', 'library', '3.9']
title = 'MagicMock specialisation instance can no longer be passed to new MagicMock instance'
updated_at = <Date 2020-02-11.00:03:09.479>
user = 'https://bugs.python.org/FrankHarrison'

bugs.python.org fields:

activity = <Date 2020-02-11.00:03:09.479>
actor = 'Elena.Oat'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-02-07.09:38:41.606>
creator = 'Frank Harrison'
dependencies = []
files = []
hgrepos = []
issue_num = 39578
keywords = []
message_count = 5.0
messages = ['361552', '361554', '361657', '361723', '361763']
nosy_count = 7.0
nosy_names = ['cjw296', 'michael.foord', 'Elena.Oat', 'lisroach', 'mariocj89', 'xtreak', 'Frank Harrison']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue39578'
versions = ['Python 3.8', 'Python 3.9']