RT 4.2.9 message/rfc822 subpart with disposition attachment is displayed inline

Hi,

is it correct that the content of a message subpart with Content-Type:
message/rfc822 Content-Disposition: attachment; is displayed inline
instead as an attachment?
I thought that everything with a Content-Disposition of attachment
should never displayed inline.

The message structure:

Content-Type: multipart/mixed;
  Content-Type: text/plain;
  Content-Type: message/rfc822 Content-Disposition: attachment;
    ...


Chris