Robert Morse gave the right answer in the other thread you posted in. I do remember "in the past" shenanigans, one in particular that happened to me, 1999, I think, I had 100 shares of AOL that was trading around 105 and had to be away from any internet access for the entire day. I set a regular hours stop at 100 and sell at 115. I came home that afternoon, saw AOL trading above 115 on CNBC screen while my computer was booting up. Once I got to my Datek account, obviously the trade had executed, but then saw that it had executed at $98!! Looking at my screen, seeing the intraday high and low, it had never traded below 102 even. Called Datek, they checked into it and called me back. Some off the wall exchange executed a trade by matching prices internally triggering the stop, which also went to that exchange. Clearly this was some kind of dirty trick, but the saving point was that my order was clearly marked as regular hours, and this trade executed pre-market. They put the 100 shares back in my account. The next day, AOL was NOT trading at 115, and I called them up again, and believe it or not, they agreed, and gave me the $115 that my original order should have traded.
Good times.