Using Classic Outlook on Windows for personal email, calendar, and contact management
I can confirm this began with 2212. Users still on 2211 do not have this problem.
The application seem to ignore the HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences*ShowFrom* key value.
New messages do not have this problem, only Replies and Forwards except when done from the Sent Items folder.