dovecot - Mar 2021 - Dovecot 2.3.14 - Invalid mailbox name: Name must not have '/' character

Hi,
after upgrading from Dovecot v2.3.13 to v2.3.14 I realized
that shared sub-folders, e.g. "Lieferanten/Rechnungen", cannot
be accessed anymore, although the underlying configuration
hasn't been changed at all. If I try to access such a folder
using e.g. Thunderbird the error "Invalid mailbox name: Name
must not have '/' character." is shown instead of opening the
folder.

Now I wonder if this is a bug or feature or what need to be done
to get the previous function back.

In the change notes of the latest Dovecot version I found the
following point, which might be the root cause of the problem:

  * If BROKENCHAR or listescape plugin is used, the escaped folder
    names may be slightly different from before in some situations.
    This is unlikely to cause issues, although caching clients may
    redownload the folders.

These are my shared folder configuration parameters:

  namespace {
    location = maildir:/home/imapshared:INDEXPVT=~/.imapmail/shared
    prefix = "#Shared/"
    separator = /
    subscriptions = no
    type = shared
  }

  protocol imap {
    mail_max_userip_connections = 15
    mail_plugins = " listescape"
 }


I also checked how the shared folders are returned with both Dovecot
version and cannot find any difference in the naming, except that the
v2.3.13 correctly labels one folder as "\HasChildren", which v2.3.14
doesn't?!

  v2.3.13:

    a list "#Shared/" "*"
    * LIST (\HasChildren) "/" #Shared/Lieferanten
    * LIST (\HasNoChildren) "/" #Shared/Lieferanten/Rechnungen

  v2.3.14:

    a list "#Shared/" "*"
    * LIST (\HasNoChildren) "/" #Shared/Lieferanten
    * LIST (\HasNoChildren) "/" #Shared/Lieferanten/Rechnungen

Any help/hint is highly appreciated.

Thanks
Juergen
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