Client "crashing" if i alt tab

Sometimes while i alt tab out of the game(mostly during the loading screen) the game client will crash. As in i cant get back into it. Its still there in my taskbar, its not giving me any errors i just cant open it again. Today it happened 2 times during an ARAM. First in loading screen and after that like 15 minutes into the game while i alt tabbed out for a facebook message while i was dead. I have to first close the launcher client and then the game client wich then gives me an errors message. I can then restart the game and rejoin it. Any idea whats causing this? Thanks
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