Program: 177731
Project: 177731
Buggy source:
@Override public boolean incrementToken() throws IOException {
  if (tailBuffer == null && !input.incrementToken()) {
    return false;
  }
  final char[] buffer=termAtt.buffer();
  if (tailBuffer != null) {
    System.arraycopy(tailBuffer,0,buffer,0,tailBuffer.length);
    termAtt.setLength(tailBuffer.length);
    tailBuffer=null;
  }
  int entityType=isEntity(termAtt.toString());
  if (entityType == VALID_URL) {
    keywordAttr.setKeyword(true);
    return true;
  }
  for (int i=0; i < termAtt.length(); i++) {
    buffer[i]=Character.toLowerCase(buffer[i]);
  }
  if (entityType != INVALID_ENTITY) {
    if (isEntityDelimiter(0)) {
      keywordAttr.setKeyword(true);
      return true;
    }
    for (int i=0; i < termAtt.length(); i++) {
      if (isEntityDelimiter(i)) {
        tailBuffer=Arrays.copyOfRange(buffer,i,termAtt.length());
        termAtt.setLength(i);
        break;
      }
    }
  }
 else {
    for (int i=0; i < termAtt.length(); i++) {
      if (isNonentityDelimiter(i)) {
        tailBuffer=Arrays.copyOfRange(buffer,i + 1,termAtt.length());
        termAtt.setLength(i);
        break;
      }
    }
    if (isEntity(termAtt.toString()) != INVALID_ENTITY) {
      keywordAttr.setKeyword(true);
      return true;
    }
    for (int i=0; i < termAtt.length(); i++) {
      if (isEntityDelimiter(i)) {
        tailBuffer=Arrays.copyOfRange(buffer,i + 1,termAtt.length());
        termAtt.setLength(i);
        break;
      }
    }
  }
  removeNonAlphanumeric();
  return true;
}

Fixed version (ground truth):
@Override public boolean incrementToken() throws IOException {
  if (tailBuffer == null && tailBufferSaved == null && !input.incrementToken()) {
    return false;
  }
  final char[] buffer=termAtt.buffer();
  if (tailBuffer != null) {
    System.arraycopy(tailBuffer,0,buffer,0,tailBuffer.length);
    termAtt.setLength(tailBuffer.length);
    tailBuffer=null;
  }
 else   if (tailBufferSaved != null) {
    System.arraycopy(tailBufferSaved,0,buffer,0,tailBufferSaved.length);
    termAtt.setLength(tailBufferSaved.length);
    tailBufferSaved=null;
  }
  int entityType=isEntity(termAtt.toString());
  if (entityType == VALID_URL) {
    keywordAttr.setKeyword(true);
    return true;
  }
  if (entityType != INVALID_ENTITY) {
    for (int i=0; i < termAtt.length(); i++) {
      buffer[i]=Character.toLowerCase(buffer[i]);
    }
    if (isEntityDelimiter(0)) {
      keywordAttr.setKeyword(true);
      return true;
    }
    for (int i=0; i < termAtt.length(); i++) {
      if (isEntityDelimiter(i)) {
        tailBuffer=Arrays.copyOfRange(buffer,i,termAtt.length());
        termAtt.setLength(i);
        break;
      }
    }
  }
 else {
    for (int i=0; i < termAtt.length(); i++) {
      if (isNonentityDelimiter(i)) {
        tailBuffer=Arrays.copyOfRange(buffer,i + 1,termAtt.length());
        termAtt.setLength(i);
        break;
      }
    }
    if (isEntity(termAtt.toString()) != INVALID_ENTITY) {
      keywordAttr.setKeyword(true);
      for (int i=0; i < termAtt.length(); i++) {
        buffer[i]=Character.toLowerCase(buffer[i]);
      }
      return true;
    }
    for (int i=0; i < termAtt.length(); i++) {
      if (isEntityDelimiter(i)) {
        if (tailBuffer != null) {
          tailBufferSaved=tailBuffer;
        }
        tailBuffer=Arrays.copyOfRange(buffer,i + 1,termAtt.length());
        termAtt.setLength(i);
        break;
      }
    }
    for (int i=0; i < termAtt.length(); i++) {
      buffer[i]=Character.toLowerCase(buffer[i]);
    }
  }
  removeNonAlphanumeric();
  return true;
}