[Baertram]

Sounds like a Clear of the table for the list was not done, unless you press the rescan button.
So check the rescan function what it does to clear the list's table, and then do the same on open of the UI so it does not duplicate the entries anymore.

briefly looking at the code it should be the function

IA_InventoryAssistant:Refresh ( reload )

So check where IA_InventoryAssistant is created via <objectName> = IA_InventoryAssistant:New

and then where <objectName>:Refresh(<reload>) is called (should be in the rescan function).
And call the same at the open of the list then.

But to tell you the truth: The code is way to complex to fix that "simply". So better switch to anoher addon please, as it's too old imo.