I changed some prices in my shop and hit the update button, then had to step away from my computer for a few minutes to make my kid her lunch. When I got back, I saw that I had an error -- this item's price can not be updated -- and when I reloaded my shop, the prices were all completely scrambled and random.
Repeated efforts to reprice everything kept taking me to the blank screen after hitting the update button. Somewhere in all of that crisis, somebody bought my Super Icy Negg for 40 NPs. (One of the scrambled, random prices that I was
trying to fix!)
(And okay, I got the thing for free when refreshing at the Advent Calendar, so it's not like I'm out actual money or anything, but still!)