While you are playing Minecraft you find a lot of strange things that damages the environment and bothers.
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Duplicate of MC-5178, please use the search function to see if your bug has already been submitted. Currently over 58% of tickets are being closed as duplicate.
this is not minecraft but mostlikely your graphics card settings.Taken from the minecraft formums:
http://www.minecraftforum.net/topic/94179-lines-between-blocks-random-graphics-glitch/
"problem is caused by antialiasing, in my case, NVIDIA's. You have to change antialising settings to "application-controlled". "