A pax wouldn't be allowed into the sterile/secured area unless they're cleared. If so, you're probably being escorted out. If that's not the case, then we have a breach.

To my understanding, it would be considered a breach if at anytime you start the screening process, then decide to leave throughout the whole ordeal without being cleared. If you're bags are still in your direct possession, or you have no bags and you're still in queue to walk through the mag yet; then technically you haven't started the screening process yet....for example the times when people come in and realize they left something in the food court or something. Once you have been screened and found clear, you're then free to move about; before then you're not clear. Look at it as somebody coming through, dropping a bag off and pulling a Carl Lewis without finishing the process; wouldn't/shouldn't that's going to raise a flag. What's he running for? What did he just come and drop the bag off? If you see a mass of people high tailing it, you're going to stand around to see what danger(s) they're running from? It's hard to explain I guess.