Nothing happened, but I had the same observation about 35 years ago while riding the train from Halifax to Montreal (via northern Maine). We were coming into an intermediate station and I was standing in one of the vestibules looking through the diaphragms. We went through a crossover and the plates of the diaphragms moved sideways enough to see daylight between them. And I thought, "Thank God for the curtains!"

Ever since then I have been concerned about making sure curtains are up and working in passenger cars in service on tourist and museum railways. And I shudder when I see them not used.

With the open vestibule ex-Lackawana coaches in use at Mid-Continent we don't allow folks to cross over once under way. We have a bungee we hang across each doorway once in motion and that works well except in the most extreme cases. mld

On the Verde Canyon Railroad, the whole point is to be able to transfer between open cars and coaches. The cars have the shelter in case of monsoon, the amenities (and, in the case of First Class, the food and plush seating) and the open cars have the canyon views which are the primary attraction (unless mileage behind a pair of slow FP7's is your thing).

That being said, I didn't pay enough attention to their (heavily-reconstructed, to be sure) passageways between cars.

On a West Chester (Pa.) RR excursion over the South Eastern Pennsylvania
Transportation Authority, passengers were told after being seated in the
coaches that they were prohibited from being in the vestibules during the
trip. The Dining Car crew wondered why they had no customers!