Link: http://trac.tools.ietf.org/wg/httpbis/trac/ticket/5
Component: p2-semantics
In the description of the Server header [section 14.38], the Via field is described as a SHOULD:
If the response is being forwarded through a proxy, the proxy application MUST NOT modify the Server response-header. Instead, it SHOULD include a Via field (as described in section 14.45).
It should be a MUST:
If the response is being forwarded through a proxy, the proxy application MUST NOT modify the Server response-header. Instead, it MUST include a Via field (as described in section 14.45).
The requirement is stated correctly in the description of the Via header, [section 14.45].
Fixed in [72]