WordPress Multisite HHVM Apache = 404s & CSS-less Dashboard

I’d really appreciate if someone can help me fix the problem I’m facing with WordPress Multisite + HHVM + Apache setup.

I’m opting for a sub-directory setup with WP running the the web-root. The problem is I can successfully create a multi-site network; but when I create a new site (other than the default), it’s dashboard is rendered without any CSS. In addition, specific pages like ‘Manage Comments’ or ‘Users’ throw a 404 ‘Page Not Found’ error.

Observations: Turning off HHVM removes the issue. So this is NOT a WP related issue, rather an HHVM related issue. I however did not find any better place to ask.

Would really appreciate your responses and help. I’ve already wasted almost a day trying to find a fix.