Program: 174534
Project: 174534
Buggy source:
@Override public void genTerrainBlocks(World world,Random rand,ChunkPrimer chunkPrimer,int chunkX,int chunkZ,double noiseVal){
  if (this.peakNoise == null || this.peakRoofNoise == null || this.worldSeed != world.getSeed()) {
    Random peakRandom=new Random(this.worldSeed);
    this.peakNoise=new NoiseGeneratorPerlin(peakRandom,4);
    this.peakRoofNoise=new NoiseGeneratorPerlin(peakRandom,1);
  }
  this.worldSeed=world.getSeed();
  double peakHeight=0.0D;
  int i=(chunkX & -128) + (chunkZ & 127);
  int j=(chunkZ & -128) + (chunkX & 127);
  double d0=Math.min(Math.abs(noiseVal) * .9,this.peakNoise.getValue((double)i * 0.5D,(double)j * 0.5D));
  if (d0 > 0.0D) {
    double d2=Math.abs(this.peakRoofNoise.getValue((double)i * 0.001953125D,(double)j * 0.001953125D));
    peakHeight=d0 * d0 * 2.5D;
    double peakOffset=Math.ceil(d2 * 50.0D) + 14.0D;
    if (peakHeight > peakOffset) {
      peakHeight=peakOffset;
    }
    peakHeight=peakHeight + 64.0D;
  }
  int x=chunkX & 15;
  int z=chunkZ & 15;
  int seaLevel=world.getSeaLevel();
  IBlockState fillerState=this.fillerBlock;
  int l=-1;
  for (int height=255; height >= 0; --height) {
    if (chunkPrimer.getBlockState(x,height,z).getMaterial() == Material.AIR && height < (int)peakHeight) {
      chunkPrimer.setBlockState(x,height,z,STONE);
    }
    if (height <= rand.nextInt(5)) {
      chunkPrimer.setBlockState(x,height,z,BEDROCK);
    }
 else {
      IBlockState iblockstate1=chunkPrimer.getBlockState(x,height,z);
      if (iblockstate1.getMaterial() == Material.AIR) {
        l=-1 - this.fillerDepth;
      }
 else       if (iblockstate1.getBlock() == Blocks.STONE) {
        if (l == -1 - this.fillerDepth) {
          chunkPrimer.setBlockState(x,height,z,this.topBlock);
          ++l;
        }
 else         if (l < 0) {
          chunkPrimer.setBlockState(x,height,z,this.fillerBlock);
          ++l;
        }
 else         if (l == 0) {
          l=1;
          chunkPrimer.setBlockState(x,height,z,this.fillerBlock);
        }
 else         if (l > 0) {
          chunkPrimer.setBlockState(x,height,z,STONE);
        }
      }
    }
  }
}

Fixed version (ground truth):
@Override public void genTerrainBlocks(World world,Random rand,ChunkPrimer chunkPrimer,int x,int z,double noiseVal){
  if (this.peakNoise == null || this.peakRoofNoise == null || this.worldSeed != world.getSeed()) {
    Random peakRandom=new Random(this.worldSeed);
    this.peakNoise=new NoiseGeneratorPerlin(peakRandom,16);
    this.peakRoofNoise=new NoiseGeneratorPerlin(peakRandom,4);
  }
  this.worldSeed=world.getSeed();
  double peakHeight=0.0D;
  int i=(x & -16) + (z & 15);
  int j=(z & -16) + (x & 15);
  double d0=Math.min(Math.abs(noiseVal),this.peakNoise.getValue((double)i * 0.5D,(double)j * 0.5D));
  if (d0 > 0.0D) {
    double d2=Math.abs(this.peakRoofNoise.getValue((double)i * 0.001953125D,(double)j * 0.001953125D));
    peakHeight=d0 * d0 * 2.5D;
    double peakOffset=Math.ceil(d2 * 50.0D) + 14.0D;
    if (peakHeight > peakOffset) {
      peakHeight=peakOffset;
    }
    peakHeight=peakHeight + 64.0D;
  }
  int chunkX=x & 15;
  int chunkZ=z & 15;
  int seaLevel=world.getSeaLevel();
  int l=-1;
  for (int height=255; height >= 0; --height) {
    if (chunkPrimer.getBlockState(chunkX,height,chunkZ).getMaterial() == Material.AIR && height < (int)peakHeight) {
      chunkPrimer.setBlockState(chunkX,height,chunkZ,STONE);
    }
    if (height <= rand.nextInt(5)) {
      chunkPrimer.setBlockState(chunkX,height,chunkZ,BEDROCK);
    }
 else {
      IBlockState iblockstate1=chunkPrimer.getBlockState(chunkX,height,chunkZ);
      if (iblockstate1.getMaterial() == Material.AIR) {
        l=-1 - this.fillerDepth;
      }
 else       if (iblockstate1.getBlock() == Blocks.STONE) {
        if (l == -1 - this.fillerDepth) {
          chunkPrimer.setBlockState(chunkX,height,chunkZ,this.topBlock);
          ++l;
        }
 else         if (l < 0) {
          chunkPrimer.setBlockState(chunkX,height,chunkZ,this.fillerBlock);
          ++l;
        }
 else         if (l == 0) {
          l=1;
          chunkPrimer.setBlockState(chunkX,height,chunkZ,this.fillerBlock);
        }
 else         if (l > 0) {
          chunkPrimer.setBlockState(chunkX,height,chunkZ,STONE);
        }
      }
    }
  }
}