[Dovecot] dovecot IMAPS + kmail

I notice that kmail does not allow an IMAP sub-folder to be created (from an IMAPS client). When I try, kmail says this cannot be done for one of the following reasons: Your access permissions may be inadequate to perform the requested operation on this resource. The location where the folder was to be created may not exist. A protocol error or incompatibility may have occurred.

Is there any simple way of getting round this? KMail has no problem creating top-level IMAP folders.