Autofilter Is Not 100% Unique

When I use the advanced filter like this:

Dim oRange As Range

Set oRange = ActiveSheet.Range("A:A")

oRange.AdvancedFilter xlFilterCopy, , Worksheets("Sheet2").Range("B1"), True
Under certain conditions, I get one duplicated value on "Sheet2". As near as I can tell so far it is only when the first cell in my "oRange" variable has a duplicate(s) of itself elsewhere in the list. The said value then appears twice in the list (only twice out of 19 instances in my particular test).

Also, I noticed that it is automatically naming the first cell in my destination range "Extract". If I change "B1" (above) to something else and run it again it throws an error because of the duplicated name "Extract".

What am I missing? What is the purpose of the automatic naming?

It looks like I need more to guarantee that my filtered list is always 100% unique.