message: remove all variables for each step in dataman
diff: @@ -169,6 +169,8 @@ StepStatus DataManReader::BeginStep(StepMode stepMode,
  m_Serializer.GetAttributes(m_IO);
  + m_IO.RemoveAllVariables();
  +
  for (const auto &i : *m_CurrentStepMetadata)
  {
  if (i.step == static_cast<size_t>(m_CurrentStep))
  