Listbox Click Event Apparently Called Without Clicking

I am writing an application in Excel 2007 VBA (on Windows Vista) which presents the user with a series of 3 userforms, each containing a listbox. The user clicks on an item in the list box of the first form and then I use the listbox click event to process the answer and assemble the list items for the listbox in the second form. This sequence is repeated in the second form (user clicks item in listbox, click event processed and used to generate 3rd userform/listbox). This seemed to work fine at first but now in some cases after clicking an item in the first listbox, I am presented with the third listbox. Apparently a choice was made in the second list box and the third list box created based on that choice but I never was presented with the second userform/listbox.

I don't think it is related to the mechanics of clicking the mouse because it occurs repeatably as follows: I had a list (for listbox 2) that was 3 items long and everything was working. I added a fourth item. Now it consistently chooses the 3rd item in this list without ever presenting me the userform/listbox 2. If I remove the fourth item it presents me with userform/listbox 2 and I click on an item and everything works as intended.

The code for the second listbox callback is very short and simple:

Private Sub SecondListBox_Click()

Dim choice As String

choice = SecondListBox.Value
Unload Me
MakeThirdListBox (choice)

End Sub