Please post your nominations for the Best of Code Review 2016 - Exterminator category.
Answer that points out the most interesting obscure bug in the original code.
In your nomination post, please make sure to include a link to the nominated answer, as well as a short explanation of what makes that post worthy of being nominated in this category, and why it should win over the others.
Small characters at the bottom: Only one nomination per post. Nominated answers must have a creation date in 2016. Downvotes don't count. Santa reserves the right to award the top-voted nominee a special bounty as a token of appreciation on behalf of the Code Review community.