Program: 58138
Project: 58138
Buggy source:
public static PlotId getPlot(Location loc){
  int x=loc.getBlockX();
  int z=loc.getBlockZ();
  String world=loc.getWorld().getName();
  PlotWorld plotworld=PlotMain.getWorldSettings(world);
  if (plotworld == null) {
    return null;
  }
  int size=plotworld.PLOT_WIDTH + plotworld.ROAD_WIDTH;
  int pathWidthLower;
  if ((plotworld.ROAD_WIDTH % 2) == 0) {
    pathWidthLower=(int)(Math.floor(plotworld.ROAD_WIDTH / 2) - 1);
  }
 else {
    pathWidthLower=(int)Math.floor(plotworld.ROAD_WIDTH / 2);
  }
  int dx=x / size;
  int dz=z / size;
  if (x < 0) {
    dx--;
    x+=((-dx) * size);
  }
  if (z < 0) {
    dz--;
    z+=((-dz) * size);
  }
  int rx=(x) % size;
  int rz=(z) % size;
  int end=pathWidthLower + plotworld.PLOT_WIDTH;
  boolean northSouth=(rz <= pathWidthLower) || (rz > (pathWidthLower + plotworld.PLOT_WIDTH));
  boolean eastWest=(rx <= pathWidthLower) || (rx > end);
  if (northSouth && eastWest) {
    PlotId id=getPlotAbs(loc.add(plotworld.ROAD_WIDTH,0,plotworld.ROAD_WIDTH));
    Plot plot=PlotMain.getPlots(loc.getWorld()).get(id);
    if (plot == null) {
      return null;
    }
    if ((plot.settings.getMerged(0) && plot.settings.getMerged(3))) {
      return getBottomPlot(loc.getWorld(),plot).id;
    }
    return null;
  }
  if (northSouth) {
    PlotId id=getPlotAbs(loc.add(0,0,plotworld.ROAD_WIDTH));
    Plot plot=PlotMain.getPlots(loc.getWorld()).get(id);
    if (plot == null) {
      return null;
    }
    if (plot.settings.getMerged(0)) {
      return getBottomPlot(loc.getWorld(),plot).id;
    }
    return null;
  }
  if (eastWest) {
    PlotId id=getPlotAbs(loc.add(plotworld.ROAD_WIDTH,0,0));
    Plot plot=PlotMain.getPlots(loc.getWorld()).get(id);
    if (plot == null) {
      return null;
    }
    if (plot.settings.getMerged(3)) {
      return getBottomPlot(loc.getWorld(),plot).id;
    }
    return null;
  }
  PlotId id=new PlotId(dx + 1,dz + 1);
  Plot plot=PlotMain.getPlots(loc.getWorld()).get(id);
  if (plot == null) {
    return id;
  }
  return getBottomPlot(loc.getWorld(),plot).id;
}

Fixed version (ground truth):
public static PlotId getPlot(Location loc){
  int x=loc.getBlockX();
  int z=loc.getBlockZ();
  String world=loc.getWorld().getName();
  PlotWorld plotworld=PlotMain.getWorldSettings(world);
  if (plotworld == null) {
    return null;
  }
  int size=plotworld.PLOT_WIDTH + plotworld.ROAD_WIDTH;
  int pathWidthLower;
  if ((plotworld.ROAD_WIDTH % 2) == 0) {
    pathWidthLower=(int)(Math.floor(plotworld.ROAD_WIDTH / 2) - 1);
  }
 else {
    pathWidthLower=(int)Math.floor(plotworld.ROAD_WIDTH / 2);
  }
  int dx=x / size;
  int dz=z / size;
  if (x < 0) {
    dx--;
    x+=((-dx) * size);
  }
  if (z < 0) {
    dz--;
    z+=((-dz) * size);
  }
  int rx=(x) % size;
  int rz=(z) % size;
  int end=pathWidthLower + plotworld.PLOT_WIDTH;
  boolean northSouth=(rz <= pathWidthLower) || (rz > end);
  boolean eastWest=(rx <= pathWidthLower) || (rx > end);
  if (northSouth && eastWest) {
    PlotId id=getPlotAbs(loc.add(plotworld.ROAD_WIDTH,0,plotworld.ROAD_WIDTH));
    Plot plot=PlotMain.getPlots(loc.getWorld()).get(id);
    if (plot == null) {
      return null;
    }
    if ((plot.settings.getMerged(0) && plot.settings.getMerged(3))) {
      return getBottomPlot(loc.getWorld(),plot).id;
    }
    return null;
  }
  if (northSouth) {
    PlotId id=getPlotAbs(loc.add(0,0,plotworld.ROAD_WIDTH));
    Plot plot=PlotMain.getPlots(loc.getWorld()).get(id);
    if (plot == null) {
      return null;
    }
    if (plot.settings.getMerged(0)) {
      return getBottomPlot(loc.getWorld(),plot).id;
    }
    return null;
  }
  if (eastWest) {
    PlotId id=getPlotAbs(loc.add(plotworld.ROAD_WIDTH,0,0));
    Plot plot=PlotMain.getPlots(loc.getWorld()).get(id);
    if (plot == null) {
      return null;
    }
    if (plot.settings.getMerged(3)) {
      return getBottomPlot(loc.getWorld(),plot).id;
    }
    return null;
  }
  PlotId id=new PlotId(dx + 1,dz + 1);
  Plot plot=PlotMain.getPlots(loc.getWorld()).get(id);
  if (plot == null) {
    return id;
  }
  return getBottomPlot(loc.getWorld(),plot).id;
}