Weird Problem : with Set Cookie Header

[sydub7]

When making a call to backend API from postman, the response header contains

Set-Cookie

JSESSIONID=xxa0R_yOx6ZVShMs5Oyw;

However when Apigee proxy makes a call to the same backend API with exact same header & payload we get

Set-Cookie JSESSIONID=_shared_session_1234

Has anyone seen this kind of behavior and its cause ? Thanks in advance.