dovecot - Aug 2017 - \Noselect isn't set on namespace prefix mailbox that can't be selected

Hi,

I tried using Nextcloud's Mail app to access my dovecot server (version: 
2.2.27 (c0f36b0)), and got an error. The relevant imap log is:

C: 3 LIST () "" (*) RETURN (SPECIAL-USE)
...
S: * LIST () "/" Archives
...
C: 6 STATUS Archives (MESSAGES)
S: 6 NO Mailbox isn't selectable (0.000 + 0.000 secs).
 >> Command 6 took 0.0014 seconds.
C: 7 LOGOUT
S: * BYE Logging out
S: 7 OK Logout completed (0.000 + 0.000 secs).
 >> Command 7 took 0.0021 seconds.

And the relevant part of my dovecot config:

namespace archives {
   disabled = no
   hidden = no
   ignore_on_failure = no
   inbox = no
   list = yes
   location = mbox:~/.mbox-archives
   order = 0
   prefix = Archives/
   separator = /
   subscriptions = yes
   type = private
}

Since ~/.mbox-archives is a directory, not a regular file, I'd expect 
dovecot to set the \Noselect attribute on the Archives folder. Is there 
something I'm missing? I tried using special_use, but that didn't accept
\Noselect as an option.