Program: 1642
Project: 1642
Buggy source:
public MessageElement next(){
  StringBuilder str=new StringBuilder();
  int i=this.bufferIndex;
  for (; i < this.buffer.length; ++i) {
    if (this.buffer[i] == ESCAPE_CHAR) {
      int nb=countEscaping(i);
      int iNext=i + nb;
      if (iNext == this.buffer.length) {
        i=iNext;
        break;
      }
 else {
        if (isMessageIndex(iNext) > iNext) {
          str.append(this.buffer,this.bufferIndex,iNext - 1 - this.bufferIndex);
          i=iNext;
          this.bufferIndex=i;
          if (nb > 1) {
            this.previousWasDoubleEscaped=true;
            this.currentMessageElement=new MessageString(str.toString());
            return this.currentMessageElement;
          }
        }
 else {
          i=iNext;
        }
      }
    }
 else     if (this.buffer[i] == ARGUMENT_START) {
      int iNext=isMessageIndex(i);
      if (iNext != i) {
        if (this.bufferIndex == i) {
          String messageIndexString=new String(this.buffer,i,iNext - i);
          int messageIndex;
          if (this.translations && messageIndexString.length() > 2) {
            messageIndex=Integer.parseInt(messageIndexString.substring(1,messageIndexString.length() - 1));
          }
 else {
            messageIndex=this.currentMessageIndex;
          }
          ++this.currentMessageIndex;
          if (this.previousWasDoubleEscaped) {
            this.currentMessageElement=new MessageIndex("String_Node_Str" + messageIndexString,messageIndex);
          }
 else {
            this.currentMessageElement=new MessageIndex(messageIndexString,messageIndex);
          }
          this.bufferIndex=iNext;
          return this.currentMessageElement;
        }
 else {
          this.currentMessageElement=new MessageString(new String(this.buffer,this.bufferIndex,i - this.bufferIndex));
          this.bufferIndex=i;
          return this.currentMessageElement;
        }
      }
    }
  }
  if (i == this.bufferIndex) {
    return null;
  }
  this.currentMessageElement=new MessageString(new String(this.buffer,this.bufferIndex,i - this.bufferIndex));
  this.bufferIndex=i;
  return this.currentMessageElement;
}

Fixed version (ground truth):
public MessageElement next(){
  StringBuilder str=new StringBuilder();
  int i=this.bufferIndex;
  for (; i < this.buffer.length; ++i) {
    if (this.buffer[i] == ESCAPE_CHAR) {
      int nb=countEscaping(i);
      int iNext=i + nb;
      if (iNext == this.buffer.length) {
        i=iNext;
        break;
      }
 else {
        if (isMessageIndex(iNext) > iNext) {
          str.append(this.buffer,this.bufferIndex,iNext - 1 - this.bufferIndex);
          i=iNext;
          this.bufferIndex=i;
          if (nb > 1) {
            this.previousWasDoubleEscaped=true;
            this.currentMessageElement=new MessageString(str.toString());
            return this.currentMessageElement;
          }
        }
 else {
          i=iNext;
        }
      }
    }
 else     if (this.buffer[i] == ARGUMENT_START) {
      int iNext=isMessageIndex(i);
      if (iNext != i) {
        if (this.bufferIndex == i) {
          String messageIndexString=String.valueOf(this.buffer,i,iNext - i);
          int messageIndex;
          if (this.translations && messageIndexString.length() > 2) {
            messageIndex=Integer.parseInt(messageIndexString.substring(1,messageIndexString.length() - 1));
          }
 else {
            messageIndex=this.currentMessageIndex;
          }
          ++this.currentMessageIndex;
          if (this.previousWasDoubleEscaped) {
            this.currentMessageElement=new MessageIndex("String_Node_Str" + messageIndexString,messageIndex);
          }
 else {
            this.currentMessageElement=new MessageIndex(messageIndexString,messageIndex);
          }
          this.bufferIndex=iNext;
          return this.currentMessageElement;
        }
 else {
          this.currentMessageElement=new MessageString(String.valueOf(this.buffer,this.bufferIndex,i - this.bufferIndex));
          this.bufferIndex=i;
          return this.currentMessageElement;
        }
      }
    }
  }
  if (i == this.bufferIndex) {
    return null;
  }
  this.currentMessageElement=new MessageString(String.valueOf(this.buffer,this.bufferIndex,i - this.bufferIndex));
  this.bufferIndex=i;
  return this.currentMessageElement;
}