It happen to me also, I was online and I press start so the car was in "Auto-pilot" then I press again on start so can continue my game, but no the car was still in auto-pilot but now it give full throttle lap after lap.
I only ever got this glitch when I literally charge into the pits. I would sometimes completely miss the stop and continue as the AI until a lap passes, before it goes back into the pits.