These things happen. Unfortunately there is no reliable way to test a new attraction under continuous guest load without... um... guests... lol. There is a big difference between simulations and real world when it comes to these rides. You can engineer something till the cows come home, but some problems just don't show up until it has been running for 12 hours straight. Combine that with budget constraints, and UM insisting an attraction opens on time - as promised - and wa-la! The more realistic and "Wow!" factor they put into these attractions, the higher the probability there will be issues. I don't want to date myself here... but... when the 'Back to the Future' 3D simulator ride was built at US, we actually got to ride it a month before the official opening. It was termed a 'technical rehearsal', and they would run it for an hour or two, then stop to evaluate comments from random riders, then open for another couple hours. With today's social media and the internet, it would be really hard to do that without too much data coming out about the attraction. Disney's policy of pretty much letting you video or take pictures of anything and everything works against them if they want to try and test something with the public before it officially opens while keeping elements a secret (other than verbal descriptions).