Guessing mailbox special use should not apply to sub-folders

Expected behavior

When you have multiple Inbox (or Archive/Sent/Etc) folders in sub-directories, they are just displayed as top level folders in the UI. This is very confusing as they all appear with the same name. For example, if I have the following folders:

Inbox
Sent
My Backups
old_email/Inbox
old_email/Sent
old_email/Other

I would expect them to be listed like that, with the "old_email/Inbox" as a drop down under "old_email".

Actual behavior

Instead (from the example), I get the following:

Inbox
Inbox
Sent
Sent
My Backups
old_email/Other

The only way to differentiate which folder is which is by clicking the ... menu item.

Mail app

Mail app version: 1.6.0

Mailserver or service: IMAP (self hosted)

Server configuration

Operating system: nextcloud upstream docker container

Web server: apache2

Database: mariadb

PHP version: 7.4.12

Nextcloud Version: 20.0.1

Client configuration

Browser: Firefox 81.0.1

Operating system: OpenSUSE tumbleweed

The issue names no files, tests, or entry points. Start by locating the code that guesses IMAP special-use folders and renders the mailbox tree, then reproduce the case with nested Inbox and Sent folders. Done means nested special-use folders remain under their parent instead of appearing as duplicate top-level folders, with coverage for the reported example.