indexes never existed because these mboxes were never used by dovecot, its not conversion from one format to another, its import.dsync(admin): Error: Failed to sync mailbox sent-mail-feb-2012: Mailbox GUIDs are not permanent without index files Well, you can work around if by letting it create indexes. Hm. Why exactly can't it create indexes? Do you have some setting disabling them?
Maybe open bug to add feature "dsync import" which will not depend on existing indexes?
