Vb.net / DataGridView / ComboBox Column

I am using vb.net and winforms.

I have a Form with a Bound DataGridView. On the DGV I have 5 columns with ComboBox. I am using the EditingControlShowing Even to catch the ComboBox Selection. (see code bellow).
Here is the problem:

After I click on a Cell with a ComboBox and make a Selection and then update the underlying cell (cell = selected value) and then click on another Row of the DGV it goes haywire. If after I update the Cell I do and EndEdit on the corresponding row of the DataSource it seems to work find.

How can I determine whe corresponding Data Source row so that I can automate this?

Private Sub dataGridView1_EditingControlShowing(ByVal sender As Object, ByVal e As DataGridViewEditingControlShowingEventArgs) _
                Handles DataGridView1.EditingControlShowing
        Try
            Debug.Print("entered the EditingControlShowing")
            Dim ColName As String = Me.DataGridView1.Columns(Me.DataGridView1.CurrentCell.ColumnIndex).Name
            If ColName = "Col1" Then 'Or ColName = "Col2" Or ColName = "Col3" Or ColName = "Col4" Or ColName = "Col5" Then

'the column you want to cast
        Dim cmb As ComboBox = TryCast(e.Control, ComboBox)
            RemoveHandler cmb.SelectedIndexChanged, AddressOf cmb_SelectedIndexChanged
            AddHandler cmb.SelectedIndexChanged, AddressOf cmb_SelectedIndexChanged
        End If
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Sub

Sub cmb_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
    Try
        Me.DataGridView1.Rows(Me.DataGridView1.CurrentRow.Index).Cells(Me.DataGridView1.CurrentCell.ColumnIndex).Value = CType(sender, ComboBox).SelectedItem
        '
        ' HERE IF I PUT MyDataSet.Tables(0).Rows(?).EndEding it works - but how to konw what row?
        '
        UpdateAvgColumn(Me.DataGridView1.CurrentRow.Index)
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Sub