Hey Footman,
Are you running Parallels on your Mac to get Windows 7?
I ask because you said same machine, which means this could just be related to the graphics card and not tied to the OS.
In order to write a bug report for this issue, could you please provide me with screenshots when in the Viewport versus while playing?
Since I am not able to reproduce this issue on my end, I need as much concrete evidence as possible so the developers can assess the issues and attempt to find a resolution.
Thank you,