difflib reports incorrect location of mismatch

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-02-10.14:11:58.219>
labels = ['3.7', '3.8', 'type-bug', 'library']
title = 'difflib reports incorrect location of mismatch'
updated_at = <Date 2019-02-11.20:07:41.441>
user = 'https://github.com/jaraco'

bugs.python.org fields:

activity = <Date 2019-02-11.20:07:41.441>
actor = 'tim.peters'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-02-10.14:11:58.219>
creator = 'jaraco'
dependencies = []
files = []
hgrepos = []
issue_num = 35955
keywords = []
message_count = 13.0
messages = ['335154', '335155', '335156', '335158', '335231', '335235', '335246', '335247', '335248', '335252', '335257', '335268', '335269']
nosy_count = 4.0
nosy_names = ['tim.peters', 'jaraco', 'chris.jerdonek', 'xtreak']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue35955'
versions = ['Python 2.7', 'Python 3.7', 'Python 3.8']