Program: 58074
Project: 58074
Buggy source:
@Override public boolean execute(final Player plr,final String... args){
  if (!PlayerFunctions.isInPlot(plr)) {
    return sendMessage(plr,C.NOT_IN_PLOT);
  }
  final Plot plot=PlayerFunctions.getCurrentPlot(plr);
  if (((plot == null) || !plot.hasOwner() || !plot.getOwner().equals(UUIDHandler.getUUID(plr))) && !PlotMain.hasPermission(plr,"String_Node_Str")) {
    return sendMessage(plr,C.NO_PLOT_PERMS);
  }
  if (PlayerFunctions.getTopPlot(plr.getWorld(),plot).equals(PlayerFunctions.getBottomPlot(plr.getWorld(),plot))) {
    return sendMessage(plr,C.UNLINK_IMPOSSIBLE);
  }
  final World world=plr.getWorld();
  final PlotId pos1=PlayerFunctions.getBottomPlot(world,plot).id;
  final PlotId pos2=PlayerFunctions.getTopPlot(world,plot).id;
  final ArrayList<PlotId> ids=PlayerFunctions.getPlotSelectionIds(pos1,pos2);
  final PlotUnlinkEvent event=new PlotUnlinkEvent(world,ids);
  Bukkit.getServer().getPluginManager().callEvent(event);
  if (event.isCancelled()) {
    event.setCancelled(true);
    PlayerFunctions.sendMessage(plr,"String_Node_Str");
    return false;
  }
  final PlotManager manager=PlotMain.getPlotManager(world);
  final PlotWorld plotworld=PlotMain.getWorldSettings(world);
  manager.startPlotUnlink(world,plotworld,ids);
  for (  final PlotId id : ids) {
    final Plot myplot=PlotMain.getPlots(world).get(id);
    if (plot == null) {
      continue;
    }
    if (plot.helpers != null) {
      myplot.helpers=plot.helpers;
    }
    if (plot.denied != null) {
      myplot.denied=plot.denied;
    }
    myplot.deny_entry=plot.deny_entry;
    myplot.settings.setMerged(new boolean[]{false,false,false,false});
    DBFunc.setMerged(world.getName(),myplot,myplot.settings.getMerged());
  }
  for (int x=pos1.x; x <= pos2.x; x++) {
    for (int y=pos1.y; y <= pos2.y; y++) {
      final boolean lx=x < pos2.x;
      final boolean ly=y < pos2.y;
      final Plot p=PlotHelper.getPlot(world,new PlotId(x,y));
      if (lx) {
        manager.createRoadEast(plotworld,p);
        if (ly) {
          manager.createRoadSouthEast(plotworld,p);
        }
      }
      if (ly) {
        manager.createRoadSouth(plotworld,p);
      }
      PlotHelper.setSign(plr.getWorld(),UUIDHandler.getName(plot.owner),plot);
    }
  }
  try {
    if (PlotHelper.canSetFast) {
      SetBlockFast.update(plr);
    }
  }
 catch (  final Exception e) {
    try {
      PlotMain.sendConsoleSenderMessage("String_Node_Str" + getClass().getMethod("String_Node_Str",Player.class,String[].class).toGenericString() + "String_Node_Str");
    }
 catch (    final Exception ex) {
      ex.printStackTrace();
    }
  }
  manager.finishPlotUnlink(world,plotworld,ids);
  PlayerFunctions.sendMessage(plr,"String_Node_Str");
  return true;
}

Fixed version (ground truth):
@Override public boolean execute(final Player plr,final String... args){
  if (!PlayerFunctions.isInPlot(plr)) {
    return sendMessage(plr,C.NOT_IN_PLOT);
  }
  final Plot plot=PlayerFunctions.getCurrentPlot(plr);
  if (((plot == null) || !plot.hasOwner() || !plot.getOwner().equals(UUIDHandler.getUUID(plr))) && !PlotMain.hasPermission(plr,"String_Node_Str")) {
    return sendMessage(plr,C.NO_PLOT_PERMS);
  }
  if (PlayerFunctions.getTopPlot(plr.getWorld(),plot).equals(PlayerFunctions.getBottomPlot(plr.getWorld(),plot))) {
    return sendMessage(plr,C.UNLINK_IMPOSSIBLE);
  }
  final World world=plr.getWorld();
  if (!unlinkPlot(world,plot)) {
    PlayerFunctions.sendMessage(plr,"String_Node_Str");
    return false;
  }
  try {
    if (PlotHelper.canSetFast) {
      SetBlockFast.update(plr);
    }
  }
 catch (  final Exception e) {
    try {
      PlotMain.sendConsoleSenderMessage("String_Node_Str" + getClass().getMethod("String_Node_Str",Player.class,String[].class).toGenericString() + "String_Node_Str");
    }
 catch (    final Exception ex) {
      ex.printStackTrace();
    }
  }
  PlayerFunctions.sendMessage(plr,"String_Node_Str");
  return true;
}