I understand the need to teach children to adapt to changing environments. But this is something that I have never experienced.
What if you were at dinner and the server brought out dessert first? Would you say "Oh well, guess they are changing it up today. What's the big deal, you will still get all of your food, right?" I doubt it.
If Mickey wanted to take pictures first, he should not have have taken the books and the pen, put them behind his back and tried to turn the kids around. I told my son that Mickey wanted pictures first. I told him that Mickey would sign his book after pictures. But he's 2 and Mickey is holding his book and his pen and refusing to sign his book. It has never happened before, and didn't happen again on the trip.
I think you're taking a pretty big leap from the order of meeting a character to the order that a meal is served. I understand you guys were upset by this but some reassurance from you and maybe some hard lessons learned for your kids will help them see that Mickey doesn't always do everything like a robot. There is some chaos involved sometimes.