mailbox.MH.add loses status info from other formats

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-11-04.22:55:29.752>
labels = ['type-bug', 'library', 'expert-email']
title = 'mailbox.MH.add loses status info from other formats'
updated_at = <Date 2017-11-04.22:55:29.752>
user = 'https://bugs.python.org/shai'

bugs.python.org fields:

activity = <Date 2017-11-04.22:55:29.752>
actor = 'shai'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)', 'email']
creation = <Date 2017-11-04.22:55:29.752>
creator = 'shai'
dependencies = []
files = []
hgrepos = []
issue_num = 31946
keywords = []
message_count = 1.0
messages = ['305572']
nosy_count = 3.0
nosy_names = ['barry', 'r.david.murray', 'shai']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue31946'
versions = ['Python 3.6']