Just look at this pathetic screen shot. I am in promos, with friends... we wait 8 minutes. And when entering the champ select, there it goes, client all bugged, impossible to do anything since if I kill it it's a dodge.
Plus, friend of mine and I could also observe that on an alt tab, a black screen in game is frequent, I even had a blue screen of death once.
I have counted 4 loss due to a similar bug. I never had these issues with previous client.