Program: 17694
Project: 17694
Buggy source:
public boolean generate(World world,Random random,int x,int y,int z){
  int type=1;
  int height=random.nextInt(4) + 1;
  boolean flag=true;
  if (y >= 1 && y + height + 1 < 256) {
    int blockID;
    int posY;
    int range;
    int posX;
    for (blockID=y; blockID <= y + 1 + height; ++blockID) {
      byte b0=3;
      if (blockID <= y + 3) {
        b0=0;
      }
      for (posY=x - b0; posY <= x + b0 && flag; ++posY) {
        for (range=z - b0; range <= z + b0 && flag; ++range) {
          if (blockID >= 0 && blockID < 256) {
            Block block=world.getBlock(posY,blockID,range);
            if (posX != 0 && block != null && !block.isLeaves(world,posY,blockID,range)) {
              flag=false;
            }
          }
 else {
            flag=false;
          }
        }
      }
    }
    if (!flag) {
      return false;
    }
 else {
      Block blockb=world.getBlock(x,y - 1,z);
      if (blockb != Blocks.mycelium && blockb != Blocks.netherrack && blockb != NContent.taintedSoil && blockb != Blocks.soul_sand) {
        return false;
      }
 else {
        int heightPos=y + height - 1;
        for (posY=heightPos; posY <= y + height; ++posY) {
          range=2;
          if (posY < y + height) {
            ++range;
          }
          for (posX=x - range; posX <= x + range; ++posX) {
            for (int posZ=z - range; posZ <= z + range; ++posZ) {
              int meta=5;
              if (posX == x - range) {
                --meta;
              }
              if (posX == x + range) {
                ++meta;
              }
              if (posZ == z - range) {
                meta-=3;
              }
              if (posZ == z + range) {
                meta+=3;
              }
              if (type == 1 || posY < y + height) {
                int swap=posY < y + height ? 2 : 1;
                if (type == 1) {
                  if ((posX == x - range || posX == x + range) && (posZ == z - range || posZ == z + range)) {
                    continue;
                  }
                }
                if (posY < y + height) {
                  if ((posX <= x - range + 1 || posX >= x + range - 1) && (posZ <= z - range + 1 || posZ >= z + range - 1)) {
                    continue;
                  }
                }
                if (posX == x - (range - swap) && posZ == z - range) {
                  meta=1;
                }
                if (posX == x - range && posZ == z - (range - swap)) {
                  meta=1;
                }
                if (posX == x + (range - swap) && posZ == z - range) {
                  meta=3;
                }
                if (posX == x + range && posZ == z - (range - swap)) {
                  meta=3;
                }
                if (posX == x - (range - swap) && posZ == z + range) {
                  meta=7;
                }
                if (posX == x - range && posZ == z + (range - swap)) {
                  meta=7;
                }
                if (posX == x + (range - swap) && posZ == z + range) {
                  meta=9;
                }
                if (posX == x + range && posZ == z + (range - swap)) {
                  meta=9;
                }
              }
              if (meta == 5 && posY < y + height) {
                meta=0;
              }
              Block block=world.getBlock(posX,posY,posZ);
              if ((meta != 0 || y >= y + height - 1) && (block == null || block.canBeReplacedByLeaves(world,posX,posY,posZ))) {
                world.setBlock(posX,posY,posZ,NContent.glowshroomPurple,meta,0);
              }
            }
          }
        }
        world.setBlock(x - 2,y + height - 1,z - 2,NContent.glowshroomPurple,1,0);
        world.setBlock(x + 2,y + height - 1,z - 2,NContent.glowshroomPurple,3,0);
        world.setBlock(x - 2,y + height - 1,z + 2,NContent.glowshroomPurple,7,0);
        world.setBlock(x + 2,y + height - 1,z + 2,NContent.glowshroomPurple,9,0);
        for (posY=0; posY < height; ++posY) {
          Block block=world.getBlock(x,y + posY,z);
          ;
          if (block == null || block.canBeReplacedByLeaves(world,x,y + posY,z)) {
            world.setBlock(x,y + posY,z,NContent.glowshroomPurple,10,0);
          }
        }
        return true;
      }
    }
  }
 else {
    return false;
  }
}

Fixed version (ground truth):
public boolean generate(World world,Random random,int x,int y,int z){
  int type=1;
  int height=random.nextInt(4) + 1;
  boolean flag=true;
  if (y >= 1 && y + height + 1 < 256) {
    int blockID;
    int posY;
    int range;
    int posX=0;
    for (blockID=y; blockID <= y + 1 + height; ++blockID) {
      byte b0=3;
      if (blockID <= y + 3) {
        b0=0;
      }
      for (posY=x - b0; posY <= x + b0 && flag; ++posY) {
        for (range=z - b0; range <= z + b0 && flag; ++range) {
          if (blockID >= 0 && blockID < 256) {
            Block block=world.getBlock(posY,blockID,range);
            if (posX != 0 && block != null && !block.isLeaves(world,posY,blockID,range)) {
              flag=false;
            }
          }
 else {
            flag=false;
          }
        }
      }
    }
    if (!flag) {
      return false;
    }
 else {
      Block blockb=world.getBlock(x,y - 1,z);
      if (blockb != Blocks.mycelium && blockb != Blocks.netherrack && blockb != NContent.taintedSoil && blockb != Blocks.soul_sand) {
        return false;
      }
 else {
        int heightPos=y + height - 1;
        for (posY=heightPos; posY <= y + height; ++posY) {
          range=2;
          if (posY < y + height) {
            ++range;
          }
          for (posX=x - range; posX <= x + range; ++posX) {
            for (int posZ=z - range; posZ <= z + range; ++posZ) {
              int meta=5;
              if (posX == x - range) {
                --meta;
              }
              if (posX == x + range) {
                ++meta;
              }
              if (posZ == z - range) {
                meta-=3;
              }
              if (posZ == z + range) {
                meta+=3;
              }
              if (type == 1 || posY < y + height) {
                int swap=posY < y + height ? 2 : 1;
                if (type == 1) {
                  if ((posX == x - range || posX == x + range) && (posZ == z - range || posZ == z + range)) {
                    continue;
                  }
                }
                if (posY < y + height) {
                  if ((posX <= x - range + 1 || posX >= x + range - 1) && (posZ <= z - range + 1 || posZ >= z + range - 1)) {
                    continue;
                  }
                }
                if (posX == x - (range - swap) && posZ == z - range) {
                  meta=1;
                }
                if (posX == x - range && posZ == z - (range - swap)) {
                  meta=1;
                }
                if (posX == x + (range - swap) && posZ == z - range) {
                  meta=3;
                }
                if (posX == x + range && posZ == z - (range - swap)) {
                  meta=3;
                }
                if (posX == x - (range - swap) && posZ == z + range) {
                  meta=7;
                }
                if (posX == x - range && posZ == z + (range - swap)) {
                  meta=7;
                }
                if (posX == x + (range - swap) && posZ == z + range) {
                  meta=9;
                }
                if (posX == x + range && posZ == z + (range - swap)) {
                  meta=9;
                }
              }
              if (meta == 5 && posY < y + height) {
                meta=0;
              }
              Block block=world.getBlock(posX,posY,posZ);
              if ((meta != 0 || y >= y + height - 1) && (block == null || block.canBeReplacedByLeaves(world,posX,posY,posZ))) {
                world.setBlock(posX,posY,posZ,NContent.glowshroomPurple,meta,0);
              }
            }
          }
        }
        world.setBlock(x - 2,y + height - 1,z - 2,NContent.glowshroomPurple,1,0);
        world.setBlock(x + 2,y + height - 1,z - 2,NContent.glowshroomPurple,3,0);
        world.setBlock(x - 2,y + height - 1,z + 2,NContent.glowshroomPurple,7,0);
        world.setBlock(x + 2,y + height - 1,z + 2,NContent.glowshroomPurple,9,0);
        for (posY=0; posY < height; ++posY) {
          Block block=world.getBlock(x,y + posY,z);
          ;
          if (block == null || block.canBeReplacedByLeaves(world,x,y + posY,z)) {
            world.setBlock(x,y + posY,z,NContent.glowshroomPurple,10,0);
          }
        }
        return true;
      }
    }
  }
 else {
    return false;
  }
}