[Dovecot] mdbox index directories: bug?

Hi,

I'm using mdbox now (Dovecot 2.2.4), with indexes on a separate disk. Works fine, but the directories for indexes are also present in the storage folder, and are empty. Userdb (sql) returns this:

home /var/vmail/domains/somedomain/someuser mail mdbox:~/mdbox:INDEX=/mnt/spool/dovecot/index/somedomain/s/someuser

And the created directory structure is:

/var/vmail/domains/somedomain/someuser /mdbox /mailboxes /INBOX

/dbox-Mails /storage

/mnt/spool/dovecot/index/somedomain/s/someuser

/mailboxes /INBOX

/storage

/var/vmail/domains/somedomain/someuser/mdbox/mailboxes/* is always empty. Am I doing something wrong, or is this by design? :)

Regards, Endre