Major visual bug - Client (I'v been experiencing this for weeks now)

So, the image I linked here is a screenshot of my champ select screen.

This bug happens randomly on any part of the client (for example in the "loot" menu or in the "news" menu as well) and it happens pretty frequently. I have reported it qt least 3 or 4 times already, but it's still here. The black rectangles seem to always appear in certain "modules" of the client (for example: clickable icons, buttons, friends' list, displayed image, and so on...) and sometimes the blackness disappears if I bring the mouse above the client. (Sometimes, as in, there's about a 50-50% chance that a certain black rectangle will disappear from a certain module)

Please look into this!

(PS: it's kinda like if ulted on my client twice a day.)