Program: 58042
Project: 58042
Buggy source:
@Override public boolean createRoadSouth(final PlotWorld plotworld,final Plot plot){
  final ClassicPlotWorld dpw=(ClassicPlotWorld)plotworld;
  final Location pos1=getPlotBottomLocAbs(plotworld,plot.id);
  final Location pos2=getPlotTopLocAbs(plotworld,plot.id);
  final int sz=pos2.getZ() + 1;
  final int ez=(sz + dpw.ROAD_WIDTH) - 1;
  final int sx=pos1.getX() - 1;
  final int ex=pos2.getX() + 2;
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx,Math.min(dpw.WALL_HEIGHT,dpw.ROAD_HEIGHT) + 1,sz + 1),new Location(plotworld.worldname,ex + 1,257,ez),new PlotBlock((short)0,(byte)0));
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx + 1,0,sz),new Location(plotworld.worldname,ex,1,ez + 1),new PlotBlock((short)7,(byte)0));
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx + 1,1,sz),new Location(plotworld.worldname,ex,dpw.WALL_HEIGHT + 1,sz + 1),dpw.WALL_FILLING);
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx + 1,dpw.WALL_HEIGHT + 1,sz),new Location(plotworld.worldname,ex,dpw.WALL_HEIGHT + 2,sz + 1),dpw.WALL_BLOCK);
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx + 1,1,ez),new Location(plotworld.worldname,ex,dpw.WALL_HEIGHT + 1,ez + 1),dpw.WALL_FILLING);
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx + 1,dpw.WALL_HEIGHT + 1,ez),new Location(plotworld.worldname,ex,dpw.WALL_HEIGHT + 2,ez + 1),dpw.WALL_BLOCK);
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx + 1,1,sz + 1),new Location(plotworld.worldname,ex,dpw.ROAD_HEIGHT + 1,ez),dpw.ROAD_BLOCK);
  return true;
}

Fixed version (ground truth):
@Override public boolean createRoadSouth(final PlotWorld plotworld,final Plot plot){
  final ClassicPlotWorld dpw=(ClassicPlotWorld)plotworld;
  final Location pos1=getPlotBottomLocAbs(plotworld,plot.id);
  final Location pos2=getPlotTopLocAbs(plotworld,plot.id);
  final int sz=pos2.getZ() + 1;
  final int ez=(sz + dpw.ROAD_WIDTH) - 1;
  final int sx=pos1.getX() - 1;
  final int ex=pos2.getX() + 2;
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx,Math.min(dpw.WALL_HEIGHT,dpw.ROAD_HEIGHT) + 1,sz),new Location(plotworld.worldname,ex + 1,257,ez + 1),new PlotBlock((short)0,(byte)0));
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx + 1,0,sz),new Location(plotworld.worldname,ex,1,ez + 1),new PlotBlock((short)7,(byte)0));
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx + 1,1,sz),new Location(plotworld.worldname,ex,dpw.WALL_HEIGHT + 1,sz + 1),dpw.WALL_FILLING);
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx + 1,dpw.WALL_HEIGHT + 1,sz),new Location(plotworld.worldname,ex,dpw.WALL_HEIGHT + 2,sz + 1),dpw.WALL_BLOCK);
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx + 1,1,ez),new Location(plotworld.worldname,ex,dpw.WALL_HEIGHT + 1,ez + 1),dpw.WALL_FILLING);
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx + 1,dpw.WALL_HEIGHT + 1,ez),new Location(plotworld.worldname,ex,dpw.WALL_HEIGHT + 2,ez + 1),dpw.WALL_BLOCK);
  MainUtil.setSimpleCuboid(plotworld.worldname,new Location(plotworld.worldname,sx + 1,1,sz + 1),new Location(plotworld.worldname,ex,dpw.ROAD_HEIGHT + 1,ez),dpw.ROAD_BLOCK);
  return true;
}