I've been experiencing an odd bug since upgrading to Windows 8. Every once in a while, my minimap doesn't get displayed correctly. All minions (enemy and ally) show up as black squares, as well as a black square around the champion pictures.
This has happened twice now in probably around 25- 30 games. I don't know how to replicate this bug, though I should note that I have run the repair tool, and it still occurred (in the game r3dlog that I uploaded) I am also running League as administrator.
Hope this helps!