Program: 12691
Project: 12691
Buggy source:
public static boolean placeAt(World world,BlockPos pos,EnumFacing dir,boolean force,boolean spawner){
  int x=pos.getX();
  int y=pos.getY();
  int z=pos.getZ();
  int x1=x + (dir == EnumFacing.SOUTH ? 1 : (dir == EnumFacing.NORTH ? -1 : 0));
  int z1=z + (dir == EnumFacing.WEST ? 1 : (dir == EnumFacing.EAST ? -1 : 0));
  int x2=x + (dir == EnumFacing.WEST ? -1 : (dir == EnumFacing.NORTH ? -1 : 1));
  int z2=z + (dir == EnumFacing.SOUTH || dir == EnumFacing.WEST ? 1 : -1);
  int x3=x + (dir == EnumFacing.WEST ? -1 : (dir == EnumFacing.EAST ? 1 : 0));
  int z3=z + (dir == EnumFacing.SOUTH ? 1 : (dir == EnumFacing.NORTH ? -1 : 0));
  Block tent=ModBlocks.tent;
  Block main=ModBlocks.tentMain;
  if (force || canPlaceAt(tent,world,x,y,z) && canPlaceAt(tent,world,x1,y,z1) && canPlaceAt(tent,world,x2,y,z2)&& canPlaceAt(tent,world,x3,y,z3)) {
    boolean flag=world.setBlockState(pos,main.getDefaultState().withProperty(BlockTent.FACING,dir.getOpposite()),3);
    if (flag) {
      world.setBlockState(new BlockPos(x1,y,z1),tent.getDefaultState().withProperty(BlockTent.FACING,dir).withProperty(BlockTent.POSITION,1),3);
      world.setBlockState(new BlockPos(x2,y,z2),tent.getDefaultState().withProperty(BlockTent.FACING,dir).withProperty(BlockTent.POSITION,2),3);
      world.setBlockState(new BlockPos(x3,y,z3),tent.getDefaultState().withProperty(BlockTent.FACING,dir.getOpposite()).withProperty(BlockTent.POSITION,3),3);
      if (spawner)       ((TileTent)world.getTileEntity(pos)).setSpawn(true);
      return true;
    }
  }
  return false;
}

Fixed version (ground truth):
public static boolean placeAt(World world,BlockPos pos,EnumFacing dir,boolean force,boolean spawner){
  int x=pos.getX();
  int y=pos.getY();
  int z=pos.getZ();
  int x1=x + (dir == EnumFacing.SOUTH ? 1 : (dir == EnumFacing.NORTH ? -1 : 0));
  int z1=z + (dir == EnumFacing.WEST ? 1 : (dir == EnumFacing.EAST ? -1 : 0));
  int x2=x + (dir == EnumFacing.WEST ? -1 : (dir == EnumFacing.NORTH ? -1 : 1));
  int z2=z + (dir == EnumFacing.SOUTH || dir == EnumFacing.WEST ? 1 : -1);
  int x3=x + (dir == EnumFacing.WEST ? -1 : (dir == EnumFacing.EAST ? 1 : 0));
  int z3=z + (dir == EnumFacing.SOUTH ? 1 : (dir == EnumFacing.NORTH ? -1 : 0));
  Block tent=ModBlocks.tent;
  Block main=ModBlocks.tentMain;
  if (force || canPlaceAt(tent,world,x,y,z) && canPlaceAt(tent,world,x1,y,z1) && canPlaceAt(tent,world,x2,y,z2)&& canPlaceAt(tent,world,x3,y,z3)) {
    boolean flag=world.setBlockState(pos,main.getDefaultState().withProperty(BlockTent.FACING,dir.getOpposite()),3);
    if (flag) {
      world.setBlockState(new BlockPos(x1,y,z1),tent.getDefaultState().withProperty(BlockTent.FACING,dir).withProperty(BlockTent.POSITION,1),3);
      world.setBlockState(new BlockPos(x2,y,z2),tent.getDefaultState().withProperty(BlockTent.FACING,dir).withProperty(BlockTent.POSITION,2),3);
      world.setBlockState(new BlockPos(x3,y,z3),tent.getDefaultState().withProperty(BlockTent.FACING,dir.getOpposite()).withProperty(BlockTent.POSITION,3),3);
      if (spawner) {
        TileEntity tile=world.getTileEntity(pos);
        if (tile instanceof TileTent) {
          ((TileTent)tile).setSpawn(true);
        }
      }
      return true;
    }
  }
  return false;
}