Not sure if it's something I'm doing or just a bug. Sometimes when I pause the game and hit resume my car is restarted in my pit stall (instead of where I left off on track) completely ruining the race. I've had to restart several of my championship races due to this.
That's the world renowned R3E Infinite Improbability Drive™. Here's a video explaining how it works: Seriously tho, it's a known and hellishly annoying bug that's being worked on. For the time being you can pause your game by activating the instant replay (default hotkey is "R") in which case this won't happen.