ComboBox initial value is not resetting

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VB

When I initially display my ComboBox, using the line ...

ComboBox3.SelectedIndex = -1

... it displays as blank, as required.

However, when I have made a selection from that ComboBox and then Cancelled, so as to reset the form, the ComboBox does not display as blank but it retains the selection I previously made.

Any ideas why & how I can reset it to being Null ?

The code is as follows, fairly basic stuff :

Public Sub Tab4_Selected()

    ComboBox3.Items.Clear()

    For Each Item In ComboBox1.Items
        With ComboBox3.Items
            .Add(Item)
        End With
    Next

    ComboBox3.Items.RemoveAt(0)

    ComboBox3.SelectedIndex = -1

    Button1.Visible = True
    Button2.Visible = True
    Button11.Visible = False
    Button12.Visible = False
    Button13.Visible = False
    Label4.Visible = False
    Label5.Visible = False
    Label6.Visible = False
    Label7.Visible = False
    Label8.Visible = False
    DateTimePicker1.Visible = False
    DateTimePicker2.Visible = False
    DateTimePicker3.Visible = False
    DateTimePicker4.Visible = False
    TextBox1.Visible = False

End Sub