function changed when pickle bound method object

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-06-16.01:40:57.101>
labels = ['3.7', 'type-bug', 'library']
title = 'function changed when pickle bound method object'
updated_at = <Date 2019-06-17.21:01:20.919>
user = 'https://bugs.python.org/georgexsh'

bugs.python.org fields:

activity = <Date 2019-06-17.21:01:20.919>
actor = 'brett.cannon'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-06-16.01:40:57.101>
creator = 'georgexsh'
dependencies = []
files = ['48424']
hgrepos = []
issue_num = 37297
keywords = ['patch']
message_count = 4.0
messages = ['345721', '345776', '345867', '345872']
nosy_count = 7.0
nosy_names = ['rhettinger', 'pitrou', 'christian.heimes', 'asvetlov', 'serhiy.storchaka', 'georgexsh', 'maggyero']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue37297'
versions = ['Python 3.7']