ComboBox ListFillRange: Items Repeat in Dropdown List

I'm having trouble with items repeating in comboBox dropdown lists in Excel 2003.

I have created three inter-dependent comboBoxes such that choosing an item from one comboBox affects the available list of choices in the other two. I do this using pivot tables which, when refreshed with the selection from one comboBox, supply the ListFillRange for the other two comboBoxes. (I delete the pivot table and recreate it from scratch as a way of dealing with errors caused by a corrupted cache.)

The ListFillRange for each comboBox is a named range which is redefined each time the pivot tables are refreshed. All of this works well. I am able to redefine the two named ranges each time a selection is made from one of the comboBoxes.

When I click the dropdown for any one of the comboBoxes, I get the correct list of choices, however, trailing this list are several blank lines and then the list (or some part of it) repeats.

When I manually clear and retype the ListFillRange in the property box for the control, the dropdown list shows properly. I have tried to repeat this operation programatically in my code but it doesn't solve the problem. Can anyone explain this behavior and offer a solution? Thx.

Here's the code I am using to update the list of one of the combo boxes:

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I call this procedure as part of a combBox change event. Here's the code for that:

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