I think you can get things to work by handling the Enter event in the gridDataBoundGrid3, and explicitly adding the new row when needed.
private void gridDataBoundGrid3_Enter(object sender, EventArgs e)
{
if(this.gridDataBoundGrid3.Model.RowCount == 1)
{
this.gridDataBoundGrid3.Binder.AddNew();
this.gridDataBoundGrid3.CancelUpdate();
}
}