The decision by exchange to cancel trades are absurd and outragous. Let's say if I have P & G stock and got stop out at 50 and market continued to go down and I bought back at 40 again. and later on PG recovered to 60. what happened to my trade? if they canceled my 40$ buy order, I lost. Market is market and you cannot just undo trades. who gave them power to undo the trades? if exchange can undo, why not individual investors undo trades?
These rules have been on the books longer than you have been alive. If you don't know the rules you're playing by you shouldn't be in the game.
Two problems here: 1.If you were able to get a trade of PG in with how fast those machines were whipsawing it around then WOW !!!!!!!! AND 2.If you got filled at $40 you would be partying down because trades below $24.70 are going to be bust.