Question RE listescape and separators

[Jakob Curdes]

Hello, we just start moving a large number of mailboxes to a new dovecot 
server with dovecot 2.0.9 (from CentOS)  and sdbox as mailbox type. We 
use imapsync so there is no issue with mailbox type conversion.
However, in test runs I noted that some mail folders,e.g.  with dots in 
them, could not be transferred; dovecot says

Couldn't create folder [7.8) Personnel] from [7.8) Personnel]: 106 NO Character not allowed in mailbox name: '.'

We have the separator "/" defined for our only namespace so the dot 
should not be an issue!?
I tried to use listescape but either the plugin is not loading (how can 
I verify this?) or it does not escape the dot in the mailbox name.
The listescape settings are the defaults:

namespace {
   separator =  /
(...)
}

mail_plugins = $mail_plugins listescape

plugin {
   listescape_char = "\\"
}


What am I doing wrong? How can I make dots in mailboxes possible?

Best regards,
Jakob Curdes