Program: 178491
Project: 178491
Buggy source:
@Override public void onExecute(Message receivedMessage){
  log.fine("String_Node_Str" + receivedMessage);
  log.fine("String_Node_Str" + Element.as(nativeNode).getString());
  TreeOperation operation=(TreeOperation)receivedMessage.getOperation();
  final int position=operation.getPosition();
  final int[] path=operation.getPath();
  final Node targetNode=TreeHelper.getChildNodeFromLocator(nativeNode,path);
  if (operation instanceof TreeInsertText) {
    TreeInsertText insertText=(TreeInsertText)operation;
    String txt=String.valueOf(insertText.getText());
    Node newTextNode=com.google.gwt.dom.client.Document.get().createTextNode(txt);
    Node brElement=targetNode.getChild(0);
    if (brElement != null && brElement.getNodeName().equalsIgnoreCase("String_Node_Str")) {
      targetNode.replaceChild(newTextNode,brElement);
    }
 else     if (path.length == 1 && position == 0) {
      targetNode.appendChild(newTextNode);
    }
 else {
      Text.as(targetNode).insertData(position,txt);
    }
  }
 else   if (operation instanceof TreeDeleteText) {
    TreeDeleteText deleteText=(TreeDeleteText)operation;
    Text textNode=(Text)targetNode;
    textNode.deleteData(position,1);
  }
 else   if (operation instanceof TreeInsertParagraph) {
    TreeInsertParagraph treeInsertParagraph=(TreeInsertParagraph)operation;
    final Element p=com.google.gwt.dom.client.Document.get().createElement("String_Node_Str");
    if (nativeNode.getChildCount() == 0) {
      targetNode.insertFirst(p);
    }
 else     if (nativeNode.getChildCount() == 1 && nativeNode.getFirstChild().getNodeName().equalsIgnoreCase("String_Node_Str")) {
      log.info("String_Node_Str");
      nativeNode.replaceChild(nativeNode.getFirstChild(),p);
    }
 else     if (position == 0) {
      p.appendChild(com.google.gwt.dom.client.Document.get().createBRElement());
      Node parentNode=targetNode.getParentElement();
      if (path.length == 1 && path[0] == 0) {
        parentNode.insertBefore(p,targetNode);
      }
 else {
        parentNode.getParentNode().insertBefore(p,parentNode);
      }
    }
 else {
      log.info("String_Node_Str");
      String actualText=targetNode.getNodeValue();
      Text textNode=Text.as(targetNode);
      textNode.deleteData(0,position);
      p.setInnerText(actualText.substring(0,position));
      Node parentElement=targetNode.getParentElement();
      parentElement.getParentElement().insertBefore(p,parentElement);
    }
  }
 else   if (operation instanceof TreeNewParagraph) {
    TreeNewParagraph treeNewParagraph=(TreeNewParagraph)operation;
    final Element p=com.google.gwt.dom.client.Document.get().createElement("String_Node_Str");
    p.appendChild(com.google.gwt.dom.client.Document.get().createBRElement());
    Node parentNode=targetNode.getParentElement();
    if (path.length == 1 && path[0] == 0) {
      parentNode.insertBefore(p,targetNode);
    }
 else {
      parentNode.getParentNode().insertBefore(p,parentNode);
    }
  }
 else   if (operation instanceof TreeMergeParagraph) {
    Node p=targetNode.getParentElement();
    Node pPreviousSibling=p.getPreviousSibling();
    targetNode.removeFromParent();
    p.removeFromParent();
    Node oldTextNode=pPreviousSibling.getChild(0);
    Text newTextNode=com.google.gwt.dom.client.Document.get().createTextNode(oldTextNode.getNodeValue() + targetNode.getNodeValue());
    pPreviousSibling.replaceChild(newTextNode,oldTextNode);
  }
  log.fine("String_Node_Str" + Element.as(nativeNode).getString());
}

Fixed version (ground truth):
@Override public void onExecute(Message receivedMessage){
  log.fine("String_Node_Str" + receivedMessage);
  log.fine("String_Node_Str" + Element.as(nativeNode).getString());
  TreeOperation operation=(TreeOperation)receivedMessage.getOperation();
  final int position=operation.getPosition();
  final int[] path=operation.getPath();
  final Node targetNode=TreeHelper.getChildNodeFromLocator(nativeNode,path);
  final short targetNodeType=targetNode.getNodeType();
  if (operation instanceof TreeInsertText) {
    TreeInsertText insertText=(TreeInsertText)operation;
    String txt=String.valueOf(insertText.getText());
    if (Node.ELEMENT_NODE == targetNodeType) {
      Node newTextNode=Document.get().createTextNode(txt);
      Node node=targetNode.getChild(position);
      targetNode.insertBefore(newTextNode,node);
    }
 else     if (Node.TEXT_NODE == targetNodeType) {
      Text.as(targetNode).insertData(position,txt);
    }
  }
 else   if (operation instanceof TreeDeleteText) {
    TreeDeleteText deleteText=(TreeDeleteText)operation;
    if (Node.TEXT_NODE == targetNodeType) {
      Text textNode=Text.as(targetNode);
      textNode.deleteData(position,1);
    }
  }
 else   if (operation instanceof TreeInsertParagraph) {
    TreeInsertParagraph treeInsertParagraph=(TreeInsertParagraph)operation;
    final Element p=Document.get().createElement("String_Node_Str");
    if (nativeNode.getChildCount() == 0) {
      targetNode.insertFirst(p);
    }
 else     if (nativeNode.getChildCount() == 1 && nativeNode.getFirstChild().getNodeName().equalsIgnoreCase("String_Node_Str")) {
      log.info("String_Node_Str");
      nativeNode.replaceChild(nativeNode.getFirstChild(),p);
    }
 else     if (position == 0) {
      p.appendChild(Document.get().createBRElement());
      Node parentNode=targetNode.getParentElement();
      if (path.length == 1 && path[0] == 0) {
        parentNode.insertBefore(p,targetNode);
      }
 else {
        parentNode.getParentNode().insertBefore(p,parentNode);
      }
    }
 else {
      log.info("String_Node_Str");
      String actualText=targetNode.getNodeValue();
      Text textNode=Text.as(targetNode);
      textNode.deleteData(0,position);
      p.setInnerText(actualText.substring(0,position));
      Node parentElement=targetNode.getParentElement();
      parentElement.getParentElement().insertBefore(p,parentElement);
    }
  }
 else   if (operation instanceof TreeNewParagraph) {
    TreeNewParagraph treeNewParagraph=(TreeNewParagraph)operation;
    final Element p=Document.get().createElement("String_Node_Str");
    p.appendChild(Document.get().createBRElement());
    Node parentNode=targetNode.getParentElement();
    if (path.length == 1 && path[0] == 0) {
      parentNode.insertBefore(p,targetNode);
    }
 else {
      parentNode.getParentNode().insertBefore(p,parentNode);
    }
  }
 else   if (operation instanceof TreeMergeParagraph) {
    Node p=targetNode.getParentElement();
    Node pPreviousSibling=p.getPreviousSibling();
    targetNode.removeFromParent();
    p.removeFromParent();
    Node oldTextNode=pPreviousSibling.getChild(0);
    Text newTextNode=Document.get().createTextNode(oldTextNode.getNodeValue() + targetNode.getNodeValue());
    pPreviousSibling.replaceChild(newTextNode,oldTextNode);
  }
 else   if (operation instanceof TreeStyle) {
    TreeStyle style=(TreeStyle)operation;
    Node parentElement=targetNode.getParentElement();
    Element styleElement=DOM.createElement(style.param);
    styleElement.appendChild(targetNode);
    parentElement.replaceChild(styleElement,targetNode);
  }
  log.fine("String_Node_Str" + Element.as(nativeNode).getString());
}