I have a VB.NET application and it is for data entry. There are several ComboBox components and only recently I changed going backwards trough the form with Left arrow to PageUp, since pressing Left/Right arrows decreases/increases value in the ComboBox.

I have this new code with PageUp for my components:

Code:
    Private Sub cboPol_GotFocus(ByVal eventSender As System.Object, ByVal eventArgs As System.EventArgs) Handles cboPol.GotFocus
        cboPol.SelectAll()
    End Sub

    Private Sub cboPol_KeyDown(ByVal eventSender As System.Object, ByVal eventArgs As System.Windows.Forms.KeyEventArgs) Handles cboPol.KeyDown
        Dim KeyCode As Short = eventArgs.KeyCode
        Dim Shift As Short = eventArgs.KeyData \ &H10000

        If KeyCode = Keys.PageUp Then
            meEmb.Focus()
        End If
    End Sub

    Private Sub cboPol_KeyPress(ByVal eventSender As System.Object, ByVal eventArgs As System.Windows.Forms.KeyPressEventArgs) Handles cboPol.KeyPress
        Dim KeyAscii As Short = Asc(eventArgs.KeyChar)

        If KeyAscii = Keys.Enter Or KeyAscii = Keys.PageDown Then

            If cboPol.Text = "" Then
                obrazecZaVnesRef.proverkaCelObrazec = True
                cboPol.Focus()
                MsgBox(SV20_MessagesModule.VNESETE_POL_MSG, MsgBoxStyle.Information)
            Else
                obrazecZaVnesRef.pol = vbNetUtilsDZS.convertToPositiveInteger(cboPol.SelectedItem)
                meRNasmes.Focus()
            End If
        End If

        eventArgs.KeyChar = Chr(KeyAscii)

        If KeyAscii = 0 Then
            eventArgs.Handled = True
        End If
    End Sub

    Private Sub cboPol_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cboPol.SelectedIndexChanged
        obrazecZaVnesRef.pol = vbNetUtilsDZS.convertToPositiveInteger(cboPol.SelectedItem)
    End Sub
Though it seems promising, PageUp changes the value in a ComboBox once you have selected with mouse different value then it was.

Which keyboard button can be used to jump trough fields of a Form backwards in the field list without affecting the previously selected value in the ComboBox components?

Or somehow I can prevent changing ComboBox components from changing its value when jumping to other field?