ProxyPreserveHost to rescue

If you set a proxy on Apache to another web server hosting an application that depends on the host in Request-URI (e.g. Phabricator) you can explicitily tell the Apache to preserve the host from the original request:

ProxyPreserveHost On

(http://httpd.apache.org/docs/2.2/mod/mod_proxy.html#proxypreservehost)