I just read this article and it is unsettling. Basically, a couple paid $2000 to cruise through the Panama Canal. Then at the last minute, Carnival changed the itinerary. This happened to me on my cruise in the Bahamas, and although I was bummed to miss the "private island," I understood that the waters were too rough for the tender boat. The port we ended up at instead was sub par, but whatever, the cruise was a few hundred bucks if I recall. But if you are looking forward to going through the Panama Canal, and then you end up only visiting some lame Caribbean islands, that is a huge difference. But apparently it's completely within Carnival's right to do such a thing. That's awful.
The article is here if you wish to read further.