When forwarding a mail as attachment, a composer window will open. That composer window shows the forwarded mail as an attachment in the attachment list. In that list, the "Name" column is empty. In KMail 1, it contained "forwarded mail". Not sure if the bug is in the messagecomposer or kmail.
Works here, cannot reproduce. Both forwarding a normal mail and forwarding a mail with an attachment.
Seems to have been fixed in the meantime :)