When moving one of my projects to iOS 7, I had a strange effect: In this App, I needed a button, that had to change its size. In iOS 6 and Xcode 4.6.3 I had created a button in the interface editor and I could now change its size and always adjust its center as well. In iOS7, this was not possible, obviously because xcode or the run time system always generated a new constraint on how to lay out the button – although I had not given it any constraints. The default was obviously to always get the default constraints.
I experimented a little and came to no better conclusion than to do the button dynamically in the code. Worked perfectly and was possible with little effort as well. Seems, I still have to get used to the constraints system.