Program: 178515
Project: 178515
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();
  Mutation mutation=new Mutation();
  final String locator=TreeUtils.getStringLocatorFromPath(operation.getPath());
  mutation.setLocator(locator);
  MutationOperator operator=new DefaultMutationOperator();
  if (operation instanceof TreeInsertText) {
    TreeInsertText tit=(TreeInsertText)operation;
    mutation.setType(Mutation.MutationType.INSERT);
    mutation.setValue(String.valueOf(position) + "String_Node_Str" + tit.getText());
    operator.operate(mutation,nativeNode);
  }
 else   if (operation instanceof TreeDeleteText) {
    TreeDeleteText treeDeleteText=(TreeDeleteText)operation;
    mutation.setType(Mutation.MutationType.REMOVE);
    mutation.setValue(String.valueOf(position) + "String_Node_Str" + String.valueOf(position + 1));
    operator.operate(mutation,nativeNode);
  }
 else   if (operation instanceof TreeInsertParagraph) {
    TreeInsertParagraph treeInsertParagraph=(TreeInsertParagraph)operation;
    Node textNode=DefaultMutationOperator.getChildNodeFromLocator(nativeNode,locator);
    String actualText=textNode.getNodeValue();
    textNode.setNodeValue(actualText.substring(0,position));
    Node n=textNode.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 textNode=DefaultMutationOperator.getChildNodeFromLocator(nativeNode,locator);
    Node p=textNode.getParentElement();
    Node n=p.getPreviousSibling();
    textNode.removeFromParent();
    p.removeFromParent();
    n.appendChild(textNode);
  }
  log.fine("String_Node_Str" + mutation);
  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();
  Mutation mutation=new Mutation();
  final String locator=TreeUtils.getStringLocatorFromPath(operation.getPath());
  mutation.setLocator(locator);
  MutationOperator operator=new DefaultMutationOperator();
  if (operation instanceof TreeInsertText) {
    TreeInsertText tit=(TreeInsertText)operation;
    mutation.setType(Mutation.MutationType.INSERT);
    mutation.setValue(String.valueOf(position) + "String_Node_Str" + tit.getText());
    operator.operate(mutation,nativeNode);
  }
 else   if (operation instanceof TreeDeleteText) {
    TreeDeleteText treeDeleteText=(TreeDeleteText)operation;
    mutation.setType(Mutation.MutationType.REMOVE);
    mutation.setValue(String.valueOf(position) + "String_Node_Str" + String.valueOf(position + 1));
    operator.operate(mutation,nativeNode);
  }
 else   if (operation instanceof TreeInsertParagraph) {
    TreeInsertParagraph treeInsertParagraph=(TreeInsertParagraph)operation;
    Node textNode=DefaultMutationOperator.getChildNodeFromLocator(nativeNode,locator);
    String actualText=textNode.getNodeValue();
    textNode.setNodeValue(actualText.substring(0,position));
    Node n=textNode.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 textNode=DefaultMutationOperator.getChildNodeFromLocator(nativeNode,locator);
    Node p=textNode.getParentElement();
    Node pPreviousSibling=p.getPreviousSibling();
    textNode.removeFromParent();
    p.removeFromParent();
    Node oldTextNode=pPreviousSibling.getChild(0);
    Text newTextNode=com.google.gwt.dom.client.Document.get().createTextNode(oldTextNode.getNodeValue() + textNode.getNodeValue());
    pPreviousSibling.replaceChild(newTextNode,oldTextNode);
  }
  log.fine("String_Node_Str" + mutation);
  log.fine("String_Node_Str" + Element.as(nativeNode).getString());
}