The error was in my Snazzy hat pattern. I realized late last week that I hadn't provided accurate instructions on how to make one of the stitches.
My first reaction, I believe, was typical: Mortification at the mistake. Cringing at the thought of frustrating people who carefully followed the pattern, but ended up with a hat that didn't look exactly like the photo.
So I fixed the pattern, and then stayed up late on Friday night and into Saturday morning emailing the corrected PDF to buyers on Etsy and uploading a new PDF for buyers on Ravelry.