itertools.chain behaves strangly when copied with copy.copy

GitHub fields:

assignee = 'https://github.com/serhiy-storchaka'
closed_at = None
created_at = <Date 2017-03-24.19:14:26.122>
labels = ['type-bug', 'library']
title = 'itertools.chain behaves strangly when copied with copy.copy'
updated_at = <Date 2017-04-03.18:56:13.232>
user = 'https://github.com/MSeifert04'

bugs.python.org fields:

activity = <Date 2017-04-03.18:56:13.232>
actor = 'rhettinger'
assignee = 'serhiy.storchaka'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2017-03-24.19:14:26.122>
creator = 'MSeifert'
dependencies = []
files = ['46769']
hgrepos = []
issue_num = 29897
keywords = ['patch']
message_count = 10.0
messages = ['290106', '290143', '290146', '290916', '290917', '290918', '290995', '291027', '291035', '291091']
nosy_count = 4.0
nosy_names = ['rhettinger', 'kristjan.jonsson', 'serhiy.storchaka', 'MSeifert']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue29897'
versions = ['Python 3.5', 'Python 3.6']