how come unchanged always true even if data changed

This code come from my saving button:

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DataSet ds1 = new DataSet();
DataSet ds2 = new DataSet();
DataSet ds3 = new DataSet();

//Static Dataset which contain values when my form load
ds1.Tables.Add(ModelSelectionGlobal.dsModelSelection.Tables["C"].Copy());
//this datatable contain the value of all controls when saving
ds2.Tables.Add(dt.Copy());

ds3.Merge(ds1);
ds3.AcceptChanges();
//now ds1 supposed to be the reference
ds3.Merge(ds2);
//ds2 contain the same structure as ds1 but may have different values

//this test should tell me is ds2 changed ds1 but it does always
return true
if (ds3.HasChanges(DataRowState.Unchanged) == false)
{
     for (int y = 0; y <= 31; y++)
     {
           //filling data with datarows of dt
           ModelSelectionGlobal.dsModelSelection.Tables["C"].Rows[0]
[y] = dr[y];
     }
}
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what im doing wrong here ?