Expecting correct host request header when proxy uri has different host then the original call

Using spring-cloud-gateway-mvc-3.1.6.jar

I built an endpoint using (mvc) ProxyExchange like in the example of the documentation: https://cloud.spring.io/spring-cloud-gateway/reference/html/#building-a-simple-gateway-by-using-spring-mvc-or-webflux

@RestController
@SpringBootApplication
public class GatewaySampleApplication {

    @Value("${remote.home}")
    private URI home;

    @GetMapping("/test")
    public ResponseEntity<?> proxy(ProxyExchange<byte[]> proxy) throws Exception {
        return proxy.uri(home.toString() + "/image/png").get();
    }

}

However, the problem I face is that if the endpoint is called from a host e.g. abc.com and then the value of ${remote.home} is def.com, then the proxy or underlying restTemplate more or less invokes the request using abc.com both as host and forward request header, whereas I expected def.com as host request header value and abc.com as forward request header value.
This also then ends up in a 403 response.

As a workaround I used proxy.sensitive("host"). This forced restTemplate to set a host request header for me again and surprise, the host request header is then the host of the ${remote.home} URI.

Or what also worked is using proxy.header(HttpHeaders.HOST, home.getHost()) by setting the host name of the ${remote.home} URI directly.

Is this supposed to work like this? I just expected that the host request header is automatically set correct if host differs from origin host.

Start with the MVC ProxyExchange entry point and the underlying RestTemplate request handling described in the report. Reproduce the /test endpoint with an incoming host different from remote.home, then trace the Host and forwarding headers. Done means the differing target and origin hosts are handled as expected, with regression coverage for the reported 403 case.