Alt+tab crash

Using alt+tab in the loading screen randomly crashes my game. It doesn't happen every time, but sometimes when I use alt+tab to check a website when I use alt+tab to get back to league the game is crashed and I just get a black screen. Then when I have the black screen I can't use alt+tab to get back or even ctrl+alt+delete and try to use task manager to shut down league even that won't come up. There's definitely a bug with the client, doesn't happen for other games ever. It's happened to me on 2 different computers, and I've gotten the leaverbuster for the 3rd time now because of this.