Possible different behaviour of explicit and implicit __dict__ accessing when involving builtin types' __dict__ descriptors

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-06-29.09:57:04.232>
labels = ['interpreter-core', 'type-bug']
title = "Possible different behaviour of explicit and implicit __dict__ accessing when involving builtin types' __dict__ descriptors"
updated_at = <Date 2016-09-27.10:13:50.266>
user = 'https://github.com/zhangyangyu'

bugs.python.org fields:

activity = <Date 2016-09-27.10:13:50.266>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2016-06-29.09:57:04.232>
creator = 'xiang.zhang'
dependencies = []
files = []
hgrepos = []
issue_num = 27411
keywords = []
message_count = 2.0
messages = ['269470', '277510']
nosy_count = 3.0
nosy_names = ['rhettinger', 'serhiy.storchaka', 'xiang.zhang']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue27411'
versions = ['Python 3.6']