In answering thread
"Re: how to suppress X-Backside-Transport http header (in a WS-Proxy)"
on developerWorks DataPower Forum I looked into the code and did some experiments.
While you cannot prevent "Connection" header from being returned to a client it depends whether you can for "X-Backside-Transport" and "Transfer-Encoding".
Please see the forum posting for the details.
What I learned from that is the intention for always sending X-BacksideTransport header to a client for a WSP or MPGW.
It helps to disambiguate transport failures from generated soap faults and enables guaranteed delivery protocols.