Program: 60002
Project: 60002
Buggy source:
@Override public boolean generate(World world,Random rand,int x,int y,int z){
  int treeHeight=(heightVariance <= 1 ? 0 : rand.nextInt(heightVariance)) + minHeight;
  int worldHeight=world.getHeight();
  Block block;
  if (y + treeHeight + 1 <= worldHeight) {
    int xOffset;
    int yOffset;
    int zOffset;
    if (genSurface != null && !canGenerateInBlock(world,x,y - 1,z,genSurface))     return false;
    if (y < worldHeight - treeHeight - 1) {
      if (treeChecks) {
        for (yOffset=y; yOffset <= y + 1 + treeHeight; ++yOffset) {
          int radius;
          if (yOffset >= y + 1 + treeHeight - 2) {
            radius=2;
          }
 else {
            radius=relaxedGrowth ? 0 : 1;
          }
          if (yOffset >= 0 & yOffset < worldHeight) {
            if (radius == 0) {
              block=world.getBlock(x,yOffset,z);
              if (!(block.isLeaves(world,x,yOffset,z) || block.isAir(world,x,yOffset,z) || block.isReplaceable(world,x,yOffset,z)|| block.canBeReplacedByLeaves(world,x,yOffset,z))) {
                return false;
              }
              if (!waterLoving && yOffset >= y + 1) {
                radius=1;
                for (xOffset=x - radius; xOffset <= x + radius; ++xOffset) {
                  for (zOffset=z - radius; zOffset <= z + radius; ++zOffset) {
                    block=world.getBlock(xOffset,yOffset,zOffset);
                    if (block.getMaterial().isLiquid()) {
                      return false;
                    }
                  }
                }
              }
            }
 else             for (xOffset=x - radius; xOffset <= x + radius; ++xOffset) {
              for (zOffset=z - radius; zOffset <= z + radius; ++zOffset) {
                block=world.getBlock(xOffset,yOffset,zOffset);
                if (!(block.isLeaves(world,xOffset,yOffset,zOffset) || block.isAir(world,xOffset,yOffset,zOffset) || block.canBeReplacedByLeaves(world,xOffset,yOffset,zOffset))) {
                  return false;
                }
              }
            }
          }
 else {
            return false;
          }
        }
        if (genSurface != null && !canGenerateInBlock(world,x,y - 1,z,genSurface))         return false;
        block=world.getBlock(x,y - 1,z);
        block.onPlantGrow(world,x,y - 1,z,x,y,z);
      }
      boolean r=false;
      for (yOffset=y - 3 + treeHeight; yOffset <= y + treeHeight; ++yOffset) {
        int var12=yOffset - (y + treeHeight), center=1 - var12 / 2;
        for (xOffset=x - center; xOffset <= x + center; ++xOffset) {
          int xPos=xOffset - x, t;
          xPos=(xPos + (t=xPos >> 31)) ^ t;
          for (zOffset=z - center; zOffset <= z + center; ++zOffset) {
            int zPos=zOffset - z;
            zPos=(zPos + (t=zPos >> 31)) ^ t;
            block=world.getBlock(xOffset,yOffset,zOffset);
            if (((xPos != center | zPos != center) || rand.nextInt(2) != 0 && var12 != 0) && (!treeChecks || block.isLeaves(world,xOffset,yOffset,zOffset) || block.isAir(world,xOffset,yOffset,zOffset)|| block.canBeReplacedByLeaves(world,xOffset,yOffset,zOffset))) {
              r|=generateBlock(world,xOffset + x,yOffset + y,zOffset + z,genBlock,leaves);
            }
          }
        }
      }
      for (yOffset=0; yOffset < treeHeight; ++yOffset) {
        block=world.getBlock(x,y + yOffset,z);
        if (!treeChecks || block.isAir(world,x,y + yOffset,z) || block.isLeaves(world,x,y + yOffset,z)|| block.isReplaceable(world,x,y + yOffset,z)) {
          r|=generateBlock(world,x,yOffset + y,z,genBlock,trunk);
        }
      }
      return r;
    }
  }
  return false;
}

Fixed version (ground truth):
@Override public boolean generate(World world,Random rand,int x,int y,int z){
  int treeHeight=(heightVariance <= 1 ? 0 : rand.nextInt(heightVariance)) + minHeight;
  int worldHeight=world.getHeight();
  Block block;
  if (y + treeHeight + 1 <= worldHeight) {
    int xOffset;
    int yOffset;
    int zOffset;
    if (genSurface != null && !canGenerateInBlock(world,x,y - 1,z,genSurface))     return false;
    if (y < worldHeight - treeHeight - 1) {
      if (treeChecks) {
        for (yOffset=y; yOffset <= y + 1 + treeHeight; ++yOffset) {
          int radius;
          if (yOffset >= y + 1 + treeHeight - 2) {
            radius=2;
          }
 else {
            radius=relaxedGrowth ? 0 : 1;
          }
          if (yOffset >= 0 & yOffset < worldHeight) {
            if (radius == 0) {
              block=world.getBlock(x,yOffset,z);
              if (!(block.isLeaves(world,x,yOffset,z) || block.isAir(world,x,yOffset,z) || block.isReplaceable(world,x,yOffset,z)|| block.canBeReplacedByLeaves(world,x,yOffset,z))) {
                return false;
              }
              if (!waterLoving && yOffset >= y + 1) {
                radius=1;
                for (xOffset=x - radius; xOffset <= x + radius; ++xOffset) {
                  for (zOffset=z - radius; zOffset <= z + radius; ++zOffset) {
                    block=world.getBlock(xOffset,yOffset,zOffset);
                    if (block.getMaterial().isLiquid()) {
                      return false;
                    }
                  }
                }
              }
            }
 else             for (xOffset=x - radius; xOffset <= x + radius; ++xOffset) {
              for (zOffset=z - radius; zOffset <= z + radius; ++zOffset) {
                block=world.getBlock(xOffset,yOffset,zOffset);
                if (!(block.isLeaves(world,xOffset,yOffset,zOffset) || block.isAir(world,xOffset,yOffset,zOffset) || block.canBeReplacedByLeaves(world,xOffset,yOffset,zOffset))) {
                  return false;
                }
              }
            }
          }
 else {
            return false;
          }
        }
        if (genSurface != null && !canGenerateInBlock(world,x,y - 1,z,genSurface))         return false;
        block=world.getBlock(x,y - 1,z);
        block.onPlantGrow(world,x,y - 1,z,x,y,z);
      }
      boolean r=false;
      for (yOffset=y - 3 + treeHeight; yOffset <= y + treeHeight; ++yOffset) {
        int var12=yOffset - (y + treeHeight), center=1 - var12 / 2;
        for (xOffset=x - center; xOffset <= x + center; ++xOffset) {
          int xPos=xOffset - x, t;
          xPos=(xPos + (t=xPos >> 31)) ^ t;
          for (zOffset=z - center; zOffset <= z + center; ++zOffset) {
            int zPos=zOffset - z;
            zPos=(zPos + (t=zPos >> 31)) ^ t;
            block=world.getBlock(xOffset,yOffset,zOffset);
            if (((xPos != center | zPos != center) || rand.nextInt(2) != 0 && var12 != 0) && (!treeChecks || block.isLeaves(world,xOffset,yOffset,zOffset) || block.isAir(world,xOffset,yOffset,zOffset)|| block.canBeReplacedByLeaves(world,xOffset,yOffset,zOffset))) {
              r|=generateBlock(world,xOffset,yOffset,zOffset,genBlock,leaves);
            }
          }
        }
      }
      for (yOffset=0; yOffset < treeHeight; ++yOffset) {
        block=world.getBlock(x,y + yOffset,z);
        if (!treeChecks || block.isAir(world,x,y + yOffset,z) || block.isLeaves(world,x,y + yOffset,z)|| block.isReplaceable(world,x,y + yOffset,z)) {
          r|=generateBlock(world,x,yOffset + y,z,genBlock,trunk);
        }
      }
      return r;
    }
  }
  return false;
}