Program: 96289
Project: 96289
Buggy source:
/** 
 * {@inheritDoc}
 */
public Object execute(ExecutionEvent event){
  final AbstractTestCaseEditor tce=(AbstractTestCaseEditor)Plugin.getActiveEditor();
  if (tce.getEditorHelper().requestEditableState() == JBEditorHelper.EditableState.OK) {
    final INodePO editorNode=(INodePO)tce.getEditorHelper().getEditSupport().getWorkVersion();
    if (!(tce.getTreeViewer().getSelection() instanceof IStructuredSelection)) {
      return null;
    }
    INodePO guiNode=(INodePO)((IStructuredSelection)tce.getTreeViewer().getSelection()).getFirstElement();
    if (guiNode == null) {
      return null;
    }
    final Integer index=editorNode.indexOf(guiNode);
    ISelectionListener listener=new ISelectionListener(){
      public void selectionChanged(      IWorkbenchPart part,      ISelection selection){
        if (!(selection instanceof IStructuredSelection)) {
          return;
        }
        List<Object> selectedElements=((IStructuredSelection)selection).toList();
        Collections.reverse(selectedElements);
        Iterator iter=selectedElements.iterator();
        List<IExecTestCasePO> addedElements=new ArrayList<IExecTestCasePO>();
        try {
          while (iter.hasNext()) {
            ISpecTestCasePO specTcToInsert=(ISpecTestCasePO)iter.next();
            try {
              addedElements.add(TestCaseBP.addReferencedTestCase(tce.getEditorHelper().getEditSupport(),editorNode,specTcToInsert,index));
            }
 catch (            PMException e) {
              NodeEditorInput inp=(NodeEditorInput)tce.getAdapter(NodeEditorInput.class);
              INodePO inpNode=inp.getNode();
              PMExceptionHandler.handlePMExceptionForMasterSession(e);
              tce.reOpenEditor(inpNode);
            }
          }
          tce.getEditorHelper().getEditSupport().lockWorkVersion();
          tce.getEditorHelper().setDirty(true);
          tce.setSelection(new StructuredSelection(addedElements));
        }
 catch (        PMException e1) {
          PMExceptionHandler.handlePMExceptionForEditor(e1,tce);
        }
      }
    }
;
    ISpecTestCasePO specTC=null;
    if (editorNode instanceof ISpecTestCasePO) {
      specTC=(ISpecTestCasePO)editorNode;
    }
    TestCaseTreeDialog dialog=new TestCaseTreeDialog(Plugin.getShell(),specTC,SWT.MULTI,TestCaseTreeDialog.TESTCASE);
    dialog.addSelectionListener(listener);
    dialog.setHelpAvailable(true);
    dialog.create();
    DialogUtils.setWidgetNameForModalDialog(dialog);
    Plugin.getHelpSystem().setHelp(dialog.getShell(),ContextHelpIds.TESTCASE_ADD_EXISTING);
    dialog.open();
    dialog.removeSelectionListener(listener);
  }
  return null;
}

Fixed version (ground truth):
/** 
 * {@inheritDoc}
 */
public Object execute(ExecutionEvent event){
  final AbstractTestCaseEditor tce=(AbstractTestCaseEditor)Plugin.getActiveEditor();
  if (tce.getEditorHelper().requestEditableState() == JBEditorHelper.EditableState.OK) {
    final INodePO editorNode=(INodePO)tce.getEditorHelper().getEditSupport().getWorkVersion();
    if (!(tce.getTreeViewer().getSelection() instanceof IStructuredSelection)) {
      return null;
    }
    final INodePO node=(INodePO)((IStructuredSelection)tce.getTreeViewer().getSelection()).getFirstElement();
    if (node == null) {
      return null;
    }
    ISelectionListener listener=getSelectionListener(tce,editorNode,node);
    ISpecTestCasePO specTC=null;
    if (editorNode instanceof ISpecTestCasePO) {
      specTC=(ISpecTestCasePO)editorNode;
    }
    TestCaseTreeDialog dialog=new TestCaseTreeDialog(Plugin.getShell(),specTC,SWT.MULTI,TestCaseTreeDialog.TESTCASE);
    dialog.addSelectionListener(listener);
    dialog.setHelpAvailable(true);
    dialog.create();
    DialogUtils.setWidgetNameForModalDialog(dialog);
    Plugin.getHelpSystem().setHelp(dialog.getShell(),ContextHelpIds.TESTCASE_ADD_EXISTING);
    dialog.open();
    dialog.removeSelectionListener(listener);
  }
  return null;
}