Oh how horrifying. Running martingales, while occasionally necessary, add a whole new level of “DONT MOVE” to my riding. I will get every fly, I will scratch every itch… to try and avoid a problem. I don’t use them often, but when they’re on I’m hyper aware.
Matter of fact, none of my horses are allowed to itch their face on their legs (or fence, or anything) while mounted, for any reason, ever. If they persist on a REALLY itchy itch, I will get off to allow them to satiate.