Attachment showing wrong content -type in trace.

[#1]

I am sending a request to my proxy with a file attachment in body whose content is pure json and I am setting Content-Type as "multipart/form-data". In trace though my file content-type is shown as application/octet-stream although it actually is application/json

[#2]

Attached file has a .json extension and still content type on apigee showing as application/octetstream