I find that particular, oft-repeated bug fascinating. It's a known issue, but one that seems to spread across many vendors and ad networks. I have to assume there's something very stubborn about the system design that makes it harder to fix than it feels like it should be.

(One hypothesis: Perhaps for privacy reasons or Amazon-not-wanting-to-give-away-the-whole-farm-on-sale-conversion reasons, ad networks only have visibility onto what you've seen, not whether you actually closed the purchase).