dovecot - Sep 2015 - Unsubscribe from shared mailbox

Hi,

I'm using Dovecot 2.2.13-11 (Debian Jessie) and shared namespace (to be 
old Cyrus compatible setting):

namespace {
   list = children
   location = 
maildir:/vmail/user/%%n/Maildir:INDEXPVT=/vmail/user/%n/Maildir/Shared/%%n
   prefix = user.%%n.
   separator = .
   subscriptions = yes
   type = shared
}

My account: milo
Other account: peter

After subscription, I have:
/vmail/user/milo/Maildir/Shared/peter/.INBOX/dovecot.index.pvt.log

After unsubscribe, file and folder still exists. Where Dovecot stores 
the information, that I had unsubscribed from this folder? I need this 
to analyze subscriptions over all mail acounts.

Thank you, Miloslav