Funny problem updating the database

[newtovbnet]

I have the following sub to change every cell in one column on a datagridview. I can see they all changed correctly. But then when I go update to to the database, for some funny reason, always the first cell on the column, has the old value updated into the database. Anybody know why?

Private sub changeDetailColumnValue()
    Dim i as Integer
    For i = 0 to (ds.Tables("myTable").Rows.Count - 1)
        DetaGridView.Rows(i).Cells(3).Value = "Test Completed"
    Next
End Sub