And I still can't reproduce. I can't even see the button that shows up in your screenshot:
Shows up to me PURCHASERS... for you, ADD PURCHASE. I wouldn't waste more time and would uninstall it and reinstall it. Also, disable all other plugins related to Downloads and test this alone to determine if it's a conflict with something else.
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The screenshots above is from IPS 4.4, so it is compatible with IPS 4.4.