Self explanatory. More like an issue than a bug but it would be nice to have 64 bit worlds in vanilla, considering that real infinite worlds are possible with BigInteger (albeit with preformance compromises) and long values. Someone has already technically done this in 1.2.5 and it worked just fine. Basically, the 30 million limit in current minecraft is much too small, and considering most modern processor can handle values up to 9.223 quintillion, I think Mojang can do better here.