Program: 81434
Project: 81434
Buggy source:
public void onPlayerMove(PlayerMoveEvent event){
  if (event.isCancelled())   return;
  if (Jail.prisoners.containsKey(event.getPlayer().getName().toLowerCase())) {
    JailPrisoner prisoner=Jail.prisoners.get(event.getPlayer().getName().toLowerCase());
    if (prisoner.isBeingReleased())     return;
    JailZone jail=prisoner.getJail();
    if (!jail.isInside(event.getTo())) {
      if (Settings.PlayerMoveProtectionAction.equals("String_Node_Str")) {
        if (prisoner.getGuards().size() > 0) {
          for (          Wolf w : prisoner.getGuards()) {
            if (w == null || w.isDead()) {
              prisoner.getGuards().remove(w);
              Jail.guards.remove(w);
              continue;
            }
            if (w.getTarget() == null)             w.setTarget(event.getPlayer());
            if (Settings.GuardTeleportDistance > 0 && w.getLocation().distanceSquared(w.getTarget().getLocation()) > Settings.GuardTeleportDistance)             w.teleport(w.getTarget().getLocation());
          }
        }
 else         prisoner.spawnGuards(Settings.NumberOfGuards,event.getTo(),event.getPlayer());
      }
 else       if (Settings.PlayerMoveProtectionAction.equals("String_Node_Str")) {
        prisoner.delete();
        plugin.getServer().broadcastMessage(event.getPlayer().getName() + "String_Node_Str");
        return;
      }
 else {
        if (Settings.PlayerMovePenalty > 0 && prisoner.getRemainingTime() > 0) {
          Util.Message(Settings.MessageMovePenalty,event.getPlayer());
          prisoner.setRemainingTime(prisoner.getRemainingTime() + Settings.PlayerMovePenalty * 6);
          InputOutput.UpdatePrisoner(prisoner);
        }
 else {
          Util.Message(Settings.MessageMoveNoPenalty,event.getPlayer());
        }
        Location teleport;
        if (!Settings.AlwaysTeleportIntoJailCenter && jail.isInside(event.getFrom()))         teleport=event.getFrom();
 else         teleport=prisoner.getTeleportLocation();
        event.setTo(teleport);
        event.setCancelled(true);
      }
    }
 else     if (Settings.PlayerMoveProtectionAction.equals("String_Node_Str")) {
      for (      Object o : prisoner.getGuards().toArray()) {
        Wolf w=(Wolf)o;
        prisoner.getGuards().remove(w);
        Jail.guards.remove(w);
        w.remove();
      }
    }
  }
}

Fixed version (ground truth):
public void onPlayerMove(PlayerMoveEvent event){
  if (event.isCancelled())   return;
  if (Jail.prisoners.containsKey(event.getPlayer().getName().toLowerCase())) {
    JailPrisoner prisoner=Jail.prisoners.get(event.getPlayer().getName().toLowerCase());
    if (prisoner.isBeingReleased())     return;
    JailZone jail=prisoner.getJail();
    if (!jail.isInside(event.getTo())) {
      if (Settings.PlayerMoveProtectionAction.equals("String_Node_Str")) {
        if (prisoner.getGuards().size() > 0) {
          for (          Wolf w : prisoner.getGuards().toArray(new Wolf[0])) {
            if (w == null || w.isDead()) {
              prisoner.getGuards().remove(w);
              Jail.guards.remove(w);
              continue;
            }
            if (w.getTarget() == null)             w.setTarget(event.getPlayer());
            if (Settings.GuardTeleportDistance > 0 && w.getLocation().distanceSquared(w.getTarget().getLocation()) > Settings.GuardTeleportDistance)             w.teleport(w.getTarget().getLocation());
          }
        }
 else         prisoner.spawnGuards(Settings.NumberOfGuards,event.getTo(),event.getPlayer());
      }
 else       if (Settings.PlayerMoveProtectionAction.equals("String_Node_Str")) {
        prisoner.delete();
        plugin.getServer().broadcastMessage(event.getPlayer().getName() + "String_Node_Str");
        return;
      }
 else {
        if (Settings.PlayerMovePenalty > 0 && prisoner.getRemainingTime() > 0) {
          Util.Message(Settings.MessageMovePenalty,event.getPlayer());
          prisoner.setRemainingTime(prisoner.getRemainingTime() + Settings.PlayerMovePenalty * 6);
          InputOutput.UpdatePrisoner(prisoner);
        }
 else {
          Util.Message(Settings.MessageMoveNoPenalty,event.getPlayer());
        }
        Location teleport;
        if (!Settings.AlwaysTeleportIntoJailCenter && jail.isInside(event.getFrom()))         teleport=event.getFrom();
 else         teleport=prisoner.getTeleportLocation();
        event.setTo(teleport);
      }
    }
 else     if (Settings.PlayerMoveProtectionAction.equals("String_Node_Str")) {
      for (      Object o : prisoner.getGuards().toArray()) {
        Wolf w=(Wolf)o;
        prisoner.getGuards().remove(w);
        Jail.guards.remove(w);
        w.remove();
      }
    }
  }
}