Program: 178504
Project: 178504
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();
  int position=operation.getPosition();
  final Node targetNode=TreeHelper.getChildNodeFromLocator(nativeNode,operation.getPath());
  if (operation instanceof TreeInsertText) {
    TreeInsertText insertText=(TreeInsertText)operation;
    String txt=String.valueOf(insertText.getText());
    if (targetNode == nativeNode) {
      Node textNode=com.google.gwt.dom.client.Document.get().createTextNode(txt);
      Node brElement=nativeNode.getChild(0);
      if (brElement != null) {
        nativeNode.replaceChild(textNode,brElement);
      }
 else {
        nativeNode.appendChild(textNode);
      }
    }
 else {
      targetNode.setNodeValue(targetNode.getNodeValue() + 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;
    String actualText=targetNode.getNodeValue();
    targetNode.setNodeValue(actualText.substring(0,position));
    Node n=targetNode.getParentElement();
    log.fine("String_Node_Str" + Element.as(n).getString());
    Element p=DOM.createElement("String_Node_Str");
    p.setInnerText(actualText.substring(position));
    n.getParentElement().insertAfter(p,n);
  }
 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();
  int position=operation.getPosition();
  final Node targetNode=TreeHelper.getChildNodeFromLocator(nativeNode,operation.getPath());
  if (operation instanceof TreeInsertText) {
    TreeInsertText insertText=(TreeInsertText)operation;
    String txt=String.valueOf(insertText.getText());
    if (targetNode == nativeNode) {
      Node newTextNode=com.google.gwt.dom.client.Document.get().createTextNode(txt);
      Node brElement=nativeNode.getChild(0);
      if (brElement != null) {
        nativeNode.replaceChild(newTextNode,brElement);
      }
 else {
        nativeNode.appendChild(newTextNode);
      }
    }
 else {
      ((Text)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;
    String actualText=targetNode.getNodeValue();
    targetNode.setNodeValue(actualText.substring(0,position));
    Node n=targetNode.getParentElement();
    log.fine("String_Node_Str" + Element.as(n).getString());
    Element p=DOM.createElement("String_Node_Str");
    p.setInnerText(actualText.substring(position));
    n.getParentElement().insertAfter(p,n);
  }
 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());
}