Dovecot seems to open extra namespaces

[Thorsten Hater]

Dear all,

I am slightly confused by the following log entries

...: imap(...): Debug: Namespace inbox: type=private, prefix=INBOX., sep=.,
inbox=yes, hidden=no, list=yes, subscriptions=yes location=maildir:~/Maildir
...: imap(...): Debug: maildir++: root=~/Maildir, index=, indexpvt=,
control=, inbox=~/Maildir, alt=
...: imap(...): Debug: Namespace : type=private, prefix=, sep=, inbox=no,
hidden=yes, list=no, subscriptions=no location=fail::LAYOUT=none
...: imap(...): Debug: none: root=, index=, indexpvt=, control=, inbox=,
alt=

It seems that Dovecot opens two different namespaces, despite only one
being configured in
10-mail.conf/15-mailboxes.conf. Is this normal and intended?
Further, what is the purpose of the line starting with 'none'?

Best regards,

 Thorsten

Dovecot version: 2.2.26.0 on Debian Jessie