I see a display problem since 10.1ß2, that did not exist in 10.1ß1.
I have a TabBarController going to another TabBarController going to a NavigationController and finally to a ViewController.
In iB (and in simulator), the icon set for the barItem of the Navigation controller appears (as a very small 10x10 probably) image at the left bottom corner above the tabBarItem of the tabBarController as well as in NavController (sorry, it is a bit hard to follow without screenshots).
Can anyone reproduce it ?