When we get high setting at Post Process quality in graphics settings, screen blurred annoyingly when ricochet near you or hit by zombie or a bullet. I can solve this problem with pushing video from main menu and it clears screen. After that its never recover back and reproducibility is getting higher..

http://www.youtube.com/watch?v=LmgVHN2UyWo&feature=c4-overview&list=UUSn76amoyGWT7xEU2stgVcg

At this video put it set time to 9:05 and see how this occurs..