MDN - Issue - AS2 connectivity -Content-Type: application/EDIINT

We have strange senario

We receive an EDIINT message via AS2 (NonEDI data) from partner expecting a synchronous MDN from our side using WM.
This process work well.
MDN message looks fine at our end but they received below message.

MDN message received by partner:

Content-Type: application/EDIINT; charset=UTF-8
Connection: close
Content-Length: 0

MDN content-type was set to multipart/report at our end but the MDN content-type that received as a application/EDIINT at partner side .

Actual MDN which we tried to send to partner from MWS

AS2-Version: 1.2
Date: Sat, 11 Nov 2023 08:34:39 +0000 (UTC)
Message-ID: <95389599.24341699691679354.JavaMail.admsvc_sagwm>
Content-Type: multipart/report; Report-Type=disposition-notification; boundary=“----=_Part_4308_1734485294.1699691679334”

Date: Sat, 11 Nov 2023 08:34:39 +0000 (UTC)
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

MDN for -
Message ID: 874104092.4431699565157229.JavaMail.SAG-WMQAS01$@sag-wmqa
Received on: 2023-11-11 at 08:34:39 (UTC)
Status: processed
Comment: This is not a guarantee that the message has been completely processed or understood by the receiving translator

Date: Sat, 11 Nov 2023 08:34:39 +0000 (UTC)
Content-Type: message/disposition-notification
Content-Transfer-Encoding: 7bit

Reporting-UA: webMethods Integration Server
Original-Recipient: rfc822; XXXXXXXXXXX
Final-Recipient: rfc822; XXXXXXXXXXX
Original-Message-ID: <874104092.4431699565157229.JavaMail.SAG-WMQA>
Received-content-MIC: OFz4h3iNyPROb3iFvTikwzogbVrQFjH7YcgM7IsnEmU=, sha256
Disposition: automatic-action/MDN-sent-automatically; processed


Then, what is ‘application/EDIINT’?
In what case does it occur?
Could anyone please help on this issue?