LAYOUT=fs and subfolders listing

[Dovecot at 9livesdata]

dovecot-2.2.28-1.el6_31.wing.x86_64

I've created this public shared namespace with

namespace public2 {
  type = public
  separator = .
  prefix = Public2.
  location = 
maildir:/mail/public2:INDEX=/mail/%u/public:LAYOUT=fs:DIRNAME=.store
  subscriptions = no
}

and I'm using the "imap_client_workarounds = tb-extra-mailbox-sep"

and filesystem structure listed at the end.

The problem is that with this configuration thunderbird (and 
roundcubemail) shows the Public2 namespace but empty - without any folders.
I've tried with another DIRNAME=StoR - same effect

If I will not use DIRNAME at all(and no .stor directories) TB sees the 
f1 f2 folders but not the f2/s1 subfolder. Just like it would not list 
any subfolders for subscription.

Within TB I can create subfolder say f1/mysub1 but after it's 
unsubscribed cannot be subscribed again(not shown in listing)

Can You provide any hints? I can live without the DIRNAME= but it has to 
list subfolders for subscription.

BTW: it works well without LAYOUT=fs - but it's kind of requirement here.

/mail/public2/:
drwxrwsr-x 4 nobody havemail 4096 Apr  7 15:07 f1
drwxrwsr-x 3 nobody havemail 4096 Apr  7 15:02 f2

/mail/public2/f1:
-rw-r--r-- 1 root   havemail   42 Apr  7 15:07 dovecot-acl
-r--r--r-- 1 nobody havemail    0 Oct 14  2015 dovecot-shared
-rw-rw-r-- 1 nobody havemail    0 Oct 15  2015 dovecot-uidlist
drwxrwsr-x 3 nobody havemail 4096 Apr  7 15:02 s1
drwxrws--- 5 nobody havemail 4096 Apr  7 15:02 .store

/mail/public2/f1/s1:
-rw-r--r-- 1 root   havemail   40 Oct 16  2015 dovecot-acl
-r--r--r-- 1 nobody havemail    0 Oct 14  2015 dovecot-shared
-rw-rw-r-- 1 nobody havemail    0 Oct 15  2015 dovecot-uidlist
drwxrws--- 5 nobody havemail 4096 Apr  7 15:02 .store

/mail/public2/f1/s1/.store:
drwxrws--- 2 nobody havemail 4096 Oct 15  2015 cur
drwxrws--- 2 nobody havemail 4096 Oct 15  2015 new
drwxrws--- 2 nobody havemail 4096 Oct 15  2015 tmp

/mail/public2/f1/.store:
drwxrws--- 2 nobody havemail 4096 Oct 15  2015 cur
drwxrws--- 2 nobody havemail 4096 Oct 15  2015 new
drwxrws--- 2 nobody havemail 4096 Oct 15  2015 tmp

/mail/public2/f2:
-rw-r--r-- 1 root   havemail   40 Oct 16  2015 dovecot-acl
-r--r--r-- 1 nobody havemail    0 Oct 14  2015 dovecot-shared
-rw-rw-r-- 1 nobody havemail    0 Oct 15  2015 dovecot-uidlist
drwxrws--- 5 nobody havemail 4096 Apr  7 15:02 .store

/mail/public2/f2/.store:
drwxrws--- 2 nobody havemail 4096 Oct 15  2015 cur
drwxrws--- 2 nobody havemail 4096 Oct 15  2015 new
drwxrws--- 2 nobody havemail 4096 Oct 15  2015 tmp