A few years back I rented an Opel with a manual transmission in Germany. Every time I stopped at a traffic light, the engine would die and I couldn't figure out what I was doing wrong. I kept thinking I must have forgotten to engage the clutch, but before long, I realized it would die no matter how quickly, slowly, carefully, or fully I engaged the clutch. As soon as the car came to a stop, so did the engine. A few days later, I discovered that if I released and reengaged the clutch, the engine would start right back up.
Apparently, this model of Opel has a start-stop system, intended to reduce idling when stuck in traffic. Whenever the car comes to a stop with the clutch engaged the engine shuts off. Then, pumping the clutch restarts the engine. That's all fine and good, but it sure would have been nice if someone had told me what was going on!