Section 4.3.1. states:
"The Content-Type of the MIME part containing the SOAP envelope will be text/xml for SOAP with attachments messages and ..."
This is true for SOAP 1.1 envelopes, which SOAPATTACH is about, but not for the use of SOAP 1.2. with attachments as mentioned in EBMS3CORE C.2
"The Content-Type of the MIME part containing the SOAP envelope will be text/xml for SOAP with attachments messages involving a SOAP 1.1 root MIME part, application/soap+xml for SOAP with attachments messages involving a SOAP 1.2 root MIME part , and ..."
Change to:
"The Content-Type of the MIME part containing the SOAP envelope will be text/xml for SOAP with attachments messages involving a SOAP 1.1 root MIME part, application/soap+xml for SOAP with attachments messages involving a SOAP 1.2 root MIME part , and ..."