This resulted from the sender of a message (LIASON@BITNIC) being attached
to a subsequent rejection message to an unrelated sender (ROOT@NSF).  It
happened when mail from a non-mailer node (as is NSF.BITNET) was rejected,
in which case the Sender: field was ignored and the Sender: field of the
previously-processed message was used by mistake.  This is fixed in mail
agent software being installed tomorrow.