dovecot - Mar 2014 - Hidden virtual folder

Hi,

I wanted to create a virtual folder containing all unread messages and
the threads they belong to, and this config works really fine:
> dovecot.conf:
namespace {
  type = private
  prefix = virtual/
  separator = /
  location = virtual:~/Maildir/virtual:INDEX=MEMORY
  list = children
  subscriptions = no
}
> virtual/All/dovecot-virtual:
*
-Trash
-Trash/*
-Junk
-Junk/*
-Drafts
-Drafts/*
-virtual
-virtual/*
  all
> virtual/New/dovecot-virtual:
virtual/All
  inthread refs or unseen recent

The only problem I got is that scanning all files for the virtual/All
mailbox takes too long, and I would like to keep them cached (no
INDEX=MEMORY), so I thought I'll just put virtual/All inside a second
virtual namespace. As it's a bad idea to open the All directory
manually, I could also hide the complete namespace to the user.

So I added the following to my config:
namespace {
  type = private
  prefix = virtual-all/
  separator = /
  location = virtual:~/Maildir/virtual-all/
  hidden = yes
  list = no
  subscriptions = no
}

But sadly it didn't work, a directory virtual-all/ pops up inside my
client (thunderbird/icedove).

Is hidden=yes/list=no unsupported for virtual locations, or is it me
misconfiguring dovecot? If it should matter, it's version 2.2.9, or more
specific debian 1:2.2.9-1~bpo70+1.

Thanks
Moritz