Listbox 'Sorted' Question

I have a Listbox with Sorted = True

I add items to it like this:

List1.AddItem "0000"
List1.AddItem "0000"
List1.AddItem "0000"
List1.AddItem "0000"

Later I do this:

List1.List(2) = Right("0000" & 1, 4)

Now List1 looks like this:

"0000"
"0000"
"0001"
"0000"

But I would have thought it would have looked like this:

"0000"
"0000"
"0000"
"0001"

Why didn't the listbox sort the items?