dovecot - Mar 2022 - Apple Mail behaviour: can not create sub-folders

One of my Apple Mail users recently complained his mail reader
couldn't create sub-folders -- he could only create top-level folders.
Playing around with this, I discovered that I could create folders (
as opposed to mialboxes) *if* I specified mailbox name with a trailing slash.

Has anyone come across this?  Is this related to

 
https://doc.dovecot.org/configuration_manual/mail_location/mbox/mboxchildfolders/

?

Joseph Tam <jtam.home at gmail.com>

On 01.03.22 02:18, Joseph Tam wrote:
>
> One of my Apple Mail users recently complained his mail reader
> couldn't create sub-folders -- he could only create top-level folders.
> Playing around with this, I discovered that I could create folders (
> as opposed to mialboxes) *if* I specified mailbox name with a trailing 
> slash.
>
> Has anyone come across this?? Is this related to
>
>
????https://doc.dovecot.org/configuration_manual/mail_location/mbox/mboxchildfolders/
>
>
> ?
>
> Joseph Tam <jtam.home at gmail.com>
Which path separators did were used?