[Access 2003] Why is Frame_Click event invoked when clicking ListBox control?

Scenario:
I have an option button group (unbound) which controls the recordsource property of a listbox control (for filtering). In the control group's Frame_Click event, the listbox.recordsource property is set when an optionbutton is clicked, and then the first row of the resulting recordset is selected in the listbox as follows:

Code:

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Private Sub Frame_Click()
    ListBox.Selected(0) = True
    Call ListBox_Click
End Sub

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Problem:
Upon subsequent clicking of the listbox control, the Frame_Click event is triggered, causing the first row of the listbox to be reselected. The result is an inability to select anything but the first row of the listbox. My question is, why does clicking the listbox control invoke the Frame_Click event? How can I prevent this event from executing when no click is performed?

Many thanks,
John