Several methods of collections.UserString do not return instances of UserString or its subclasses

GitHub fields:

assignee = 'https://github.com/lisroach'
closed_at = None
created_at = <Date 2017-10-22.19:46:35.040>
labels = ['3.7', 'type-bug', 'library']
title = 'Several methods of collections.UserString do not return instances of UserString or its subclasses'
updated_at = <Date 2019-05-07.10:28:33.338>
user = 'https://github.com/vaultah'

bugs.python.org fields:

activity = <Date 2019-05-07.10:28:33.338>
actor = 'vaultah'
assignee = 'lisroach'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2017-10-22.19:46:35.040>
creator = 'vaultah'
dependencies = []
files = []
hgrepos = []
issue_num = 31841
keywords = ['patch']
message_count = 4.0
messages = ['304761', '304857', '306726', '341536']
nosy_count = 4.0
nosy_names = ['rhettinger', 'vaultah', 'lisroach', 'anthony shaw']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue31841'
versions = ['Python 3.7']