Working off the latest 0.3.1 build, I had a Freya install running under VirtualBox 5.0.6, everything went great up until I installed Guest Additions (with no errors) and rebooted to a login screen with a black background (user accounts etc. still visible). Upon login, the screen shows that it verified my password, then hangs, goes black, and brings me back to this mysterious black login screen. I have a hunch elementary OS doesn't like one of the VBox drivers, is there a known fix?