Actually, the true reason Test Track breaks down is because each car is powered with as much (if not more) technology than a real shuttle. With this said, if one abnormality is detected on the ride, the cars all individually shut down. Basically, if your glasses fall off during the ride and land on the "track," then the ride will shut down until those glasses are found. If you lose a piece of food, or anything else, once one car detects it, it sends out a signal to shut all the cars down.
Hense the ever-so-frequent 101s.
PS: Just because the CMs don't tell you what the problems are, they all know. It's part of keeping the problems backstage and keeping the magic onstage.