message: delete old elements after refinement, since they have all been replaced
diff: @@ -5995,6 +5995,7 @@ void Mesh::UniformRefinement2D()
  MFEM_ABORT("unknown element type: " << el_type);
  }
  }
  + old_elements.DeleteAll();
  boundary.SetSize(2 * NumOfBdrElements);
  for (int i = 0; i < NumOfBdrElements; i++)
  