[Client] keyboard freeze in game, making hard to play smoothly

it's been till some patch now (maybe 5.2/5.3?) that, from time to time, keyboards in game refuse to react

What i mean is, for exemple with sion, pressing keyboards do nothing (no noise when spell not ready, no spell indicator, no ult activation, just nothing) So you press key again and again (could be 5-10 sec before thing go back to normal) and when it react again, all your spell you tried to use in the "zero reaction" time are use (the biggest problem being with auto cast spell like sion Q,R and similar stuff for other champ, you waste them nearly all the time :s )

I saw similar problem on forum since 5.2 for other poeple (involving mouse too) but it was supposed to be solved. Is this a client bug ( meaning I should repair it) or a known issue on your side?