Double join singleplayer world bug

When you join a singleplayer map in 1.8.7 before your map load you will be sended to the main screen for 5 seconds or so and if in this five second you join your singleplayer map a second time your game will be broken you will go trow the block its doing this for me maybe beacos i dont have a good cumputer and this bug try to load 2 map but you shud test this and try to fix it thanks log.zip