I've noticed something similar playing Mini Metro last month.
I was running a Windows 7 VM on an OS X 10.9.5 host with Virtualbox 4.2.28 using my mid 2013 Macbook Air (Intel HD Graphics 5000 1024 MB). Instead of blurring the game for the weekly upgrade menu, it showed the center of my host desktop wallpaper, upside-down and flipped (other than that, there was distortion whatsoever). It really creeped me out.
I was running a Windows 7 VM on an OS X 10.9.5 host with Virtualbox 4.2.28 using my mid 2013 Macbook Air (Intel HD Graphics 5000 1024 MB). Instead of blurring the game for the weekly upgrade menu, it showed the center of my host desktop wallpaper, upside-down and flipped (other than that, there was distortion whatsoever). It really creeped me out.
http://i.imgur.com/OqYvYjq.png