HTTP/1.1 proxy behavior when Host differs from absoluteURI

What is the correct behavior for a (forward) proxy that receives a 
request with an absoluteURI that differs from the Host header? 5.1.2 
suggests that the Host header should be ignored ("Note that the proxy 
MAY forward the request on to another proxy or /directly to the 
server////specified by the absoluteURI/"). 5.2 seems to suggest the 
same, but this section is scoped to the behavior of the origin server, 
not for a proxy.

If the Host header should be ignored for forwarding by the proxy, should 
the Host header be stripped or forwarded to the next hop?