This is interesting indeed. I haven't heard of this before. I would like to share a different kind of Upset in horse racing.
Horse racing track in our area sets up a celebration show every Fourth of July. They have pony rides for kids, fireworks, etc. A few years ago we went there on the fourth of July with friends and family.
We placed some wagers. Mainly losing ones. The last race we had a bigger amount placed on a horse (don't remember the name). Luckily for us, the horse came in first. We started celebrating. A few minutes later there was an announcement that race results were under review.
Apparently, jockeys can make an inquiry if there was some kind of violation by another jockey or a horse. The horse that won (our pick) was disqualified for a violation and placed at 4th place, which meant we lost again.
We were really UPSET. :)
That's an upsetting tale. :)