Just ran into this one, and I'm not entirely sure what's causing it, though since it's only showing up in Martyr I doubt it's a faulty hardware issue (drivers are also up to date). Running a Radeon R7950 (now with dual monitors), and after adding the second monitor today I've been having strange artifacts showing up in-game; Windows 7 64 bit, 16 gigs RAM, eight core 4.1GHz processor, hard drives are healthy, etc etc getting the usual out of the way.