During the 1900s period of the ride, Inside the Magic reports the show stopped in its tracks and the Cast Member attending the ride got on the speakers to declare a person had taken off his or her mask and the show would not begin again until the situation was rectified.
Apparently, the parkgoer in question hopped to it, because the ride began again almost immediately.
A new report from a parkgoer who recently rode The Magic Kingdom’s Carousel of Progress ride witnessed the ride stopping after one sneaky parkgoer decided to take an air-conditioned opportunity to de-mask.