ipaddress module accepts some strange IPv6 addresses that it shouldn't

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2018-08-21.20:22:58.607>
labels = ['type-bug', 'tests']
title = "ipaddress module accepts some strange IPv6 addresses that it shouldn't"
updated_at = <Date 2018-08-25.16:33:09.677>
user = 'https://bugs.python.org/lkcl'

bugs.python.org fields:

activity = <Date 2018-08-25.16:33:09.677>
actor = 'enedil'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Tests']
creation = <Date 2018-08-21.20:22:58.607>
creator = 'lkcl'
dependencies = []
files = ['47757']
hgrepos = []
issue_num = 34453
keywords = []
message_count = 9.0
messages = ['323843', '323895', '323896', '324014', '324019', '324024', '324055', '324057', '324076']
nosy_count = 5.0
nosy_names = ['lkcl', 'ncoghlan', 'pmoody', 'enedil', 'prudvinit']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34453'
versions = ['Python 3.5', 'Python 3.6']