Crashing my game

The first time it happened I was playing Survival Games on the Lichcraft server, but afterwards I tested it multiple times on other servers and in single player and the same thing happened. What happens is that when I have both the Left-Shift and tab key pressed at the same time it crashes my game, says that it is not responding and something has gone wrong. I am wondering if it is just my computer or if it is minecraft it self because I have also tested with other games and they have not crashed.