Program: 173812
Project: 173812
Buggy source:
/** 
 * Merge a minor into an already started company. <p>Also covers the actions of the Final Minor Exchange Round, in which minors can also be closed (in that case, the MergeCompanies.major attribute is null, which never occurs in normal stock rounds).
 * @param action
 * @return
 */
protected boolean mergeCompanies(MergeCompanies action){
  PublicCompanyI minor=action.getMergingCompany();
  PublicCompanyI major=action.getSelectedTargetCompany();
  PublicCertificateI cert=null;
  Portfolio pool=Bank.getPool();
  CashHolder cashDestination=null;
  MoveSet.start(true);
  if (major != null) {
    cert=major.getPortfolio().findCertificate(major,false);
    if (cert != null) {
      cashDestination=major;
    }
 else {
      cert=pool.findCertificate(major,false);
    }
  }
  int minorCash=minor.getCash();
  int minorTrains=minor.getPortfolio().getTrainList().size();
  if (cashDestination == null) {
    if (minorCash > 0)     new CashMove(minor,null,minorCash);
    pool.transferAssetsFrom(minor.getPortfolio());
  }
 else {
    major.transferAssetsFrom(minor);
  }
  MapHex homeHex=minor.getHomeHex();
  int homeCityNumber=homeHex.getCityOfBaseToken(minor);
  minor.setClosed();
  if (major != null && action.getReplaceToken()) {
    if (homeHex.layBaseToken(major,homeCityNumber)) {
      major.layBaseToken(homeHex,homeCityNumber);
    }
  }
  if (major != null) {
    checkFlotation(major);
    if (major.getNumberOfTrains() > major.getCurrentTrainLimit() && !compWithExcessTrains.contains(major)) {
      new AddToList<PublicCompanyI>(compWithExcessTrains,major,"String_Node_Str");
    }
  }
  if (cert != null) {
    ReportBuffer.add(LocalText.getText("String_Node_Str",new String[]{currentPlayer.getName(),minor.getName(),major.getName(),Bank.format(minorCash),String.valueOf(minorTrains)}));
    ReportBuffer.add(LocalText.getText("String_Node_Str",new String[]{currentPlayer.getName(),String.valueOf(cert.getShare()),major.getName(),cert.getPortfolio().getName(),minor.getName()}));
    cert.moveTo(currentPlayer.getPortfolio());
    ReportBuffer.add(LocalText.getText("String_Node_Str",minor.getName()));
  }
 else {
    ReportBuffer.add(LocalText.getText("String_Node_Str",new String[]{currentPlayer.getName(),minor.getName(),Bank.format(minorCash),String.valueOf(minorTrains)}));
  }
  hasActed.set(true);
  if (!(this instanceof FinalMinorExchangeRound)) {
    companyBoughtThisTurnWrapper.set(major);
    setPriority();
  }
  return true;
}

Fixed version (ground truth):
/** 
 * Merge a minor into an already started company. <p>Also covers the actions of the Final Minor Exchange Round, in which minors can also be closed (in that case, the MergeCompanies.major attribute is null, which never occurs in normal stock rounds).
 * @param action
 * @return
 */
protected boolean mergeCompanies(MergeCompanies action){
  PublicCompanyI minor=action.getMergingCompany();
  PublicCompanyI major=action.getSelectedTargetCompany();
  PublicCertificateI cert=null;
  Portfolio pool=Bank.getPool();
  CashHolder cashDestination=null;
  MoveSet.start(true);
  if (major != null) {
    cert=major.getPortfolio().findCertificate(major,false);
    if (cert != null) {
      cashDestination=major;
    }
 else {
      cert=pool.findCertificate(major,false);
    }
  }
  int minorCash=minor.getCash();
  int minorTrains=minor.getPortfolio().getTrainList().size();
  if (cashDestination == null) {
    if (minorCash > 0)     new CashMove(minor,null,minorCash);
    pool.transferAssetsFrom(minor.getPortfolio());
  }
 else {
    major.transferAssetsFrom(minor);
  }
  MapHex homeHex=minor.getHomeHex();
  int homeCityNumber=homeHex.getCityOfBaseToken(minor);
  minor.setClosed();
  if (major != null && action.getReplaceToken()) {
    if (homeHex.layBaseToken(major,homeCityNumber)) {
      major.layBaseToken(homeHex,homeCityNumber);
    }
  }
  if (major != null) {
    if (major.getNumberOfTrains() > major.getCurrentTrainLimit() && !compWithExcessTrains.contains(major)) {
      new AddToList<PublicCompanyI>(compWithExcessTrains,major,"String_Node_Str");
    }
  }
  if (cert != null) {
    ReportBuffer.add(LocalText.getText("String_Node_Str",new String[]{currentPlayer.getName(),minor.getName(),major.getName(),Bank.format(minorCash),String.valueOf(minorTrains)}));
    ReportBuffer.add(LocalText.getText("String_Node_Str",new String[]{currentPlayer.getName(),String.valueOf(cert.getShare()),major.getName(),cert.getPortfolio().getName(),minor.getName()}));
    cert.moveTo(currentPlayer.getPortfolio());
    ReportBuffer.add(LocalText.getText("String_Node_Str",minor.getName()));
    checkFlotation(major);
  }
 else {
    ReportBuffer.add(LocalText.getText("String_Node_Str",new String[]{currentPlayer.getName(),minor.getName(),Bank.format(minorCash),String.valueOf(minorTrains)}));
  }
  hasActed.set(true);
  if (!(this instanceof FinalMinorExchangeRound)) {
    companyBoughtThisTurnWrapper.set(major);
    setPriority();
  }
  return true;
}