I'm not sure whether last AMD Catalyst support had something to do with that...
Happens from time to time on both red and green GPU's. Just a data error of some sort that screwed up what got rendered. This one is just more apparent than most. I think it likely more a CPU or data transfer issue that screwed up synchronization of the background map and game generated objects and detail than the GPU as the GPU has rendered the picture quite well.
Well, all I can say it's dangerous. I started to worry after I actually sent worker to horse-resource on east of island.