> >Subject: Message ("Your mailing for PACS-L has been submitted to the...")
                      ^^^^^^^^^^^^^^^^^^^^^^^
>> [...]
> I don't feel this Subject: line very useful. I can't figure which mailing
> it is about.
 
See the highlighted phrase above. It includes the name of the
mailing list in the text of the subject line.
 
> This subject: line, which is produced automatically, should better have
> been a copy of the Sybject: line from *my* mailing instead of the beginning
> of the body of the list server's reply to my mailing.
> Am I right ?
 
No. This is a response generated by the server to inform you that
it has taken an action on your behalf -- it has distributed your
note to the mailing list. It has no connection with your posting
to the mailing list other than being produced as a consequence.