HHVM seems to fail on some group permission s

I'm seeing what I think is an odd bug where HHVM fails for access to a directory where:
1. The hhvm process user has group access
2. The group ownership of the directory is not the primary group for the user
3. The directory permissions are set to 770 (775 work for read always of course).

Here's a post on SO I made to see if it was just my config or something: http://stackoverflow.com/questions/22749281/hhvm-3-0-hack-with-nginx-cannot-access-file-in-directory-with-770-permissions