Why does it fail to access the cell value of a new DataGridViewRow after insertion to the DGV?

Question

I know there are a couple of ways to create a new DataGridViewRow, see How to add a new row to datagridview programmatically
I am currently creating a class that inherits from DGVR, so I cannot let the DGV create it by just adding values, I must create it manually instead.
However, my code (written in C++/CLI) failed with ArgumentOutOfRangeException, so I tried with a normal DGVR and it also failed (method 1). Then I found a solution (method 2), but I don't understand why it works.
Is the original DGVR made invalid somehow after adding it to the DGV?

{
  ... 

  DataGridViewRow^ dgvrTest = gcnew DataGridViewRow();
  dgvrTest->CreateCells (dataGridView1);
  Object^ oValue = dgvrTest->Cells[0]->Value;  // okay

  int ixRow = dataGridView1->Rows->Add (dgvrTest);
  oValue = dataGridView1->Rows[ixRow]->Cells[0]->Value;  // okay

  // method #1
  oValue = dgvrTest->Cells[0]->Value;  // fails after adding the DGVR to the DGV

  // method #2
  dgvrTest = dataGridView1->Rows[ixRow];  // receives a different object. WHY?
  oValue = dgvrTest->Cells[0]->Value;  // works
}