ctypes automatic byref failing on custom classes attributes

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-08-19.18:11:36.954>
labels = ['ctypes', 'type-feature', '3.8', '3.9', '3.10']
title = 'ctypes automatic byref failing on custom classes attributes'
updated_at = <Date 2021-03-05.19:59:59.538>
user = 'https://github.com/lepaperwan'

bugs.python.org fields:

activity = <Date 2021-03-05.19:59:59.538>
actor = 'terry.reedy'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['ctypes']
creation = <Date 2016-08-19.18:11:36.954>
creator = 'lepaperwan'
dependencies = []
files = []
hgrepos = []
issue_num = 27803
keywords = []
message_count = 4.0
messages = ['273149', '273711', '273755', '273868']
nosy_count = 5.0
nosy_names = ['amaury.forgeotdarc', 'belopolsky', 'meador.inge', 'eryksun', 'lepaperwan']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue27803'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']