Last modified: 2014-04-10 04:04:23 UTC
Full URLs like http://en.hhvm.beta.wmflabs.org/wiki/Main_Page work, but a bare request for http://en.hhvm.beta.wmflabs.org/ gets redirected to http://en.wikipedia.beta.wmflabs.org/.
$wgServer and $wgCanonicalServer were misconfigured. (The URL is now <http://en.wikipedia.beta-hhvm.wmflabs.org/wiki/Main_Page>, too, but not as a consequence of this bug.)