Program: 159382
Project: 159382
Buggy source:
@Override public PreventionEffectData preventDamage(GameEvent event,Ability source,Game game,int amountToPrevent){
  PreventionEffectData result=new PreventionEffectData(amountToPrevent);
  if (!(event instanceof DamageEvent)) {
    result.setError(true);
    return result;
  }
  DamageEvent damageEvent=(DamageEvent)event;
  GameEvent preventEvent=new GameEvent(GameEvent.EventType.PREVENT_DAMAGE,damageEvent.getTargetId(),damageEvent.getSourceId(),source.getControllerId(),damageEvent.getAmount(),false);
  if (game.replaceEvent(preventEvent)) {
    result.setReplaced(true);
    return result;
  }
  if (event.getAmount() > amountToPrevent) {
    result.setPreventedDamage(amountToPrevent);
    damageEvent.setAmount(event.getAmount() - amountToPrevent);
  }
 else {
    result.setPreventedDamage(event.getAmount());
    damageEvent.setAmount(0);
  }
  if (amountToPrevent != Integer.MAX_VALUE) {
    event.setData(Integer.toString(amountToPrevent-=result.getPreventedDamage()));
  }
  MageObject damageSource=game.getObject(damageEvent.getSourceId());
  MageObject preventionSource=game.getObject(source.getSourceId());
  if (damageSource != null && preventionSource != null) {
    MageObject targetObject=game.getObject(event.getTargetId());
    String targetName="String_Node_Str";
    if (targetObject == null) {
      Player targetPlayer=game.getPlayer(event.getTargetId());
      if (targetPlayer != null) {
        targetName=targetPlayer.getName();
      }
    }
 else {
      targetName=targetObject.getName();
    }
    StringBuilder message=new StringBuilder(preventionSource.getName()).append("String_Node_Str");
    message.append(Integer.toString(result.getPreventedDamage())).append("String_Node_Str").append(damageSource.getName());
    if (!targetName.isEmpty()) {
      message.append("String_Node_Str").append(targetName);
    }
    game.informPlayers(message.toString());
  }
  game.fireEvent(GameEvent.getEvent(GameEvent.EventType.PREVENTED_DAMAGE,damageEvent.getTargetId(),source.getSourceId(),source.getControllerId(),result.getPreventedDamage()));
  return result;
}

Fixed version (ground truth):
@Override public PreventionEffectData preventDamage(GameEvent event,Ability source,Game game,int amountToPrevent){
  PreventionEffectData result=new PreventionEffectData(amountToPrevent);
  if (!(event instanceof DamageEvent)) {
    result.setError(true);
    return result;
  }
  DamageEvent damageEvent=(DamageEvent)event;
  GameEvent preventEvent=new GameEvent(GameEvent.EventType.PREVENT_DAMAGE,damageEvent.getTargetId(),damageEvent.getSourceId(),source.getControllerId(),damageEvent.getAmount(),false);
  if (game.replaceEvent(preventEvent)) {
    result.setReplaced(true);
    return result;
  }
  if (event.getAmount() > amountToPrevent) {
    result.setPreventedDamage(amountToPrevent);
    damageEvent.setAmount(event.getAmount() - amountToPrevent);
  }
 else {
    result.setPreventedDamage(event.getAmount());
    damageEvent.setAmount(0);
  }
  if (amountToPrevent != Integer.MAX_VALUE) {
    result.setRemainingAmount(amountToPrevent-=result.getPreventedDamage());
  }
  MageObject damageSource=game.getObject(damageEvent.getSourceId());
  MageObject preventionSource=game.getObject(source.getSourceId());
  if (damageSource != null && preventionSource != null) {
    MageObject targetObject=game.getObject(event.getTargetId());
    String targetName="String_Node_Str";
    if (targetObject == null) {
      Player targetPlayer=game.getPlayer(event.getTargetId());
      if (targetPlayer != null) {
        targetName=targetPlayer.getName();
      }
    }
 else {
      targetName=targetObject.getName();
    }
    StringBuilder message=new StringBuilder(preventionSource.getName()).append("String_Node_Str");
    message.append(Integer.toString(result.getPreventedDamage())).append("String_Node_Str").append(damageSource.getName());
    if (!targetName.isEmpty()) {
      message.append("String_Node_Str").append(targetName);
    }
    game.informPlayers(message.toString());
  }
  game.fireEvent(GameEvent.getEvent(GameEvent.EventType.PREVENTED_DAMAGE,damageEvent.getTargetId(),source.getSourceId(),source.getControllerId(),result.getPreventedDamage()));
  return result;
}