It's a bit hard to explain but I've tried having it solved on the Offical forums and the guy from Riot who tried helping me couldn't quite figure it out either. That was awhile ago and it hasn't been a unplayable type of issue so I've ignored it. But now that some time has passed maybe it's just a common easy to fix issue now.
The problem is my shadows don't follow what they're shadowing and freeze every time I stop scrolling the camera. same goes for fog of war. I can be standing in fog of war and not have any vision unless I scroll the camera as if to "refresh" what I should be seeing. Now I can still see champions/minions/spells like I should, but the map looks as if I don't have vision.
You can watch a video I made on my Youtube channel to see what I'm talking about:http://www.youtube.com/user/ProvokedofLoL?feature=mhum
The very first fight is a good example of the shadows and the second fight with teemo has a great example of the fog of war.