Last weeks I did some tests involving world seeds and I discovered they do not work properly. The point of seeds should be to recreate the exact same world as someone else, correct?

When I look up a random Let's player that starts his first episode in Minecraft 1.6.2, and I use the exact same seed as him in my Minecraft 1.6.2, the world start out the same. But when I walk the same directions as the LPer, things start to change.

It only involves certain areas. Mostly deserts, plains and mountains are exactly the same, including every tree, flower and all of the high grass. Forests are also the same except for the sporadic area in which all the trees are located different.

Jungles are almost completely different. Sometimes even the dirt blocks and rocks are positioned different. Lava and Water streams sometimes differ too.

So: 90% of the world looks the same, but 10% Always looks different than someone else. I recreated the world multiple times to see if it was randomized, but my results are always exactly the same as my previous attempt.

Something is bugging my world seeds. Is it Java, the operating system or something else? I do not know, but I believe it is a bug.

I am willing to provide a link to an LPer video and multiple screens of my world to prove that there are differences in world generation with the same seed, but I won't do that now, because if this isn't a bug, I won't have to waste an hour of my time.

Thanks!