I have a retina MacBook Pro 15 inch, Mid 2012, i7 2.3ghz with 2 video cards, an Intel HD 4000 and a GeForce GT650M. Recently I noticed some video issues happening only when I use Mission Control. Some apps appear with "video artifacts" on its window. It is weird because it does not happen on the entire screen and it can happen to any app. I am afraid one of my video cards is going to fail soon. I can't reproduce the problem since it does not happen often and I am not sure if it happens only with one video card or both. Here is a screenshot of what I see. Hope anyone can help me.