dovecot - Oct 2014 - Renaming not supported across conflicting directory - why?

I wonder what is point of checkign file/dir create mode like this?

Here it makes problems since some folders have different permissions than 
others but both are accessible/writable by user. So renaming is possible (as 
renaming according to unix permissions). Yet dovecot artificially prevents 
this.


        /* if we're renaming under another mailbox, require its permissions
           to be same as ours. */
        if (strchr(newname, mailbox_list_get_hierarchy_sep(newlist)) != NULL) 
{
                struct mailbox_permissions old_perm, new_perm;

                mailbox_list_get_permissions(oldlist, oldname, &old_perm);
                mailbox_list_get_permissions(newlist, newname, &new_perm);

                if ((new_perm.file_create_mode != old_perm.file_create_mode ||
                     new_perm.dir_create_mode != old_perm.dir_create_mode ||
                     new_perm.file_create_gid != old_perm.file_create_gid)) {
                        mailbox_list_set_error(oldlist, 
MAIL_ERROR_NOTPOSSIBLE,
                                "Renaming not supported across conflicting
"
                                "directory permissions");
                        return -1;
                }
        }


-- 
Arkadiusz Mi?kiewicz, arekm / ( maven.pl | pld-linux.org )