I've experienced this in certain corners in Time Trial. Sometimes, if I mess up and allow the car to roll over a corner it doesn't take my lap away, whereas if I'm too early on the brakes, accelerate, and just manage to slip off the circuit it will pop up immediately. Not all corners are like this, and will disqualify you anyways. Like every F1 title with global leaderboards, some figure out how to cut and cheat. I remember previous titles were littered with stupid times, as you could literally go on a hike across the grass on tracks like Spa and pick up tons of time. I don't get why they do it, but it's going to happen.
The game is so much better with limits than previous titles. Still, there's certain parts you can leave the track and not get a penalty for it. It's usually in parts where going off isn't going to give you an advantage, and Codemasters were pretty smart with it. Almost like they asked former F1 drivers which corners are the main culprits.