Customising the Word 2007 Ribbon ersetting combobox after selection

Hi,
I am cutomising the ribbon in Word 2007 to have a combobox on a new tab where users can select an item and it inserts Autotext (or building blocks as they are now called) into the document. I have written the XML and the requisite VBA to do all this and it is working well. The last hurdle however is that if they select the same item in the combobox a second time, the code to insert the AutoText is not triggered. To overcome this I am trying to reset the combobox selection to "nothing" or "blank" once the AutoText is inserted. I used to be able to use control.listitem=-1, but can't get this to work.

I tried adding a "blank" entry to the list so I could select it, but can't get this to work either. Not sure what the InvalidateControl does, but obviously not what I want.
Thanks,
Penny

'Callback for Tables onChange
Sub AddTable(control As IRibbonControl, text As String)
Dim aTemplate As Template
Dim BBTemplate As Template
For Each aTemplate In Templates
    If aTemplate.Name = "MyOwnBldgBlocks.dotx" Then
        Set BBTemplate = aTemplate
        Exit For
    End If
Next aTemplate
 
    Select Case text
    Case " "
        Exit Sub
    Case "2 col table"
        BBTemplate.BuildingBlockEntries("2_pg").Insert Where _
        :=Selection.Range, RichText:=True
    Case "6 col table"
        BBTemplate.BuildingBlockEntries("6_pg").Insert Where _
        :=Selection.Range, RichText:=True
    Case "8 col table"
        BBTemplate.BuildingBlockEntries("8_pg").Insert Where _
        :=Selection.Range, RichText:=True
    End Select
    
    MyRibbon.InvalidateControl ("Tables")
 
End Sub

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