Program: 45697
Project: 45697
Buggy source:
/** 
 */
@Override public void drop(DropTargetDropEvent dtde){
  Point location=dtde.getLocation();
  TreePath path=cellHierarchyTree.getPathForLocation(location.x,location.y);
  if (path == null) {
    dtde.rejectDrop();
    return;
  }
  dtde.acceptDrop(DnDConstants.ACTION_MOVE);
  Transferable transferable=dtde.getTransferable();
  String cellIDString=null;
  try {
    DataFlavor df=new DataFlavor("String_Node_Str" + "String_Node_Str");
    cellIDString=(String)transferable.getTransferData(df);
  }
 catch (  Exception excp) {
    LOGGER.log(Level.WARNING,"String_Node_Str" + "String_Node_Str",excp);
    return;
  }
  if (cellIDString == null || cellIDString.startsWith("String_Node_Str") == false) {
    LOGGER.warning("String_Node_Str" + cellIDString);
    return;
  }
  int cellIDInt=-1;
  try {
    cellIDInt=Integer.parseInt(cellIDString.substring(7));
  }
 catch (  Exception excp) {
    LOGGER.log(Level.WARNING,"String_Node_Str" + "String_Node_Str",excp);
    return;
  }
  CellID cellID=new CellID(cellIDInt);
  WonderlandSession session=LoginManager.getPrimary().getPrimarySession();
  CellCache cache=ClientContext.getCellCache(session);
  if (cache == null) {
    LOGGER.warning("String_Node_Str" + session);
    return;
  }
  Cell draggedCell=cache.getCell(cellID);
  if (draggedCell == null) {
    LOGGER.warning("String_Node_Str" + cellID);
    return;
  }
  CellID parentCellID=CellID.getInvalidCellID();
  DefaultMutableTreeNode treeNode=(DefaultMutableTreeNode)path.getLastPathComponent();
  Object userObject=treeNode.getUserObject();
  Cell newParent=null;
  if (userObject instanceof Cell) {
    parentCellID=((Cell)userObject).getCellID();
    newParent=(Cell)userObject;
    if (draggedCell.equals(newParent) == true) {
      return;
    }
  }
  Cell oldParent=draggedCell.getParent();
  CellTransform oldParentWorld=new CellTransform(null,null);
  if (oldParent != null) {
    oldParentWorld=oldParent.getWorldTransform();
  }
  CellTransform newParentWorld=new CellTransform(null,null);
  if (newParent != null) {
    newParentWorld=newParent.getWorldTransform();
  }
  CellTransform newChildLocal=ScenegraphUtils.computeChildTransform(newParentWorld,draggedCell.getWorldTransform());
  CellEditChannelConnection connection=(CellEditChannelConnection)session.getConnection(CellEditConnectionType.CLIENT_TYPE);
  connection.send(new CellReparentMessage(cellID,parentCellID,newChildLocal));
  dragOverTreeNode=null;
  cellHierarchyTree.repaint();
}

Fixed version (ground truth):
/** 
 */
@Override public void drop(DropTargetDropEvent dtde){
  Point location=dtde.getLocation();
  TreePath path=cellHierarchyTree.getPathForLocation(location.x,location.y);
  if (path == null) {
    dtde.rejectDrop();
    return;
  }
  dtde.acceptDrop(DnDConstants.ACTION_MOVE);
  Transferable transferable=dtde.getTransferable();
  String cellIDString=null;
  try {
    DataFlavor df=new DataFlavor("String_Node_Str" + "String_Node_Str");
    cellIDString=(String)transferable.getTransferData(df);
  }
 catch (  Exception excp) {
    LOGGER.log(Level.WARNING,"String_Node_Str" + "String_Node_Str",excp);
    return;
  }
  if (cellIDString == null || cellIDString.startsWith("String_Node_Str") == false) {
    LOGGER.warning("String_Node_Str" + cellIDString);
    return;
  }
  int cellIDInt=-1;
  try {
    cellIDInt=Integer.parseInt(cellIDString.substring(7));
  }
 catch (  Exception excp) {
    LOGGER.log(Level.WARNING,"String_Node_Str" + "String_Node_Str",excp);
    return;
  }
  CellID cellID=new CellID(cellIDInt);
  WonderlandSession session=LoginManager.getPrimary().getPrimarySession();
  CellCache cache=ClientContext.getCellCache(session);
  if (cache == null) {
    LOGGER.warning("String_Node_Str" + session);
    return;
  }
  Cell draggedCell=cache.getCell(cellID);
  if (draggedCell == null) {
    LOGGER.warning("String_Node_Str" + cellID);
    return;
  }
  CellID parentCellID=CellID.getInvalidCellID();
  SortedTreeNode treeNode=(SortedTreeNode)path.getLastPathComponent();
  Object userObject=treeNode.getUserObject();
  Cell newParent=null;
  if (userObject instanceof Cell) {
    parentCellID=((Cell)userObject).getCellID();
    newParent=(Cell)userObject;
    if (draggedCell.equals(newParent) == true) {
      return;
    }
  }
  CellTransform newParentWorld=new CellTransform(null,null);
  if (newParent != null) {
    newParentWorld=newParent.getWorldTransform();
  }
  CellTransform newChildLocal=ScenegraphUtils.computeChildTransform(newParentWorld,draggedCell.getWorldTransform());
  CellEditChannelConnection connection=(CellEditChannelConnection)session.getConnection(CellEditConnectionType.CLIENT_TYPE);
  connection.send(new CellReparentMessage(cellID,parentCellID,newChildLocal));
  dragOverTreeNode=null;
  cellHierarchyTree.repaint();
}