If you open an Xcode 4.x project at Xcode 5 and then open a xib at Interface Builder, you will get an alert:
NOTE: I only have the issues with the forced iOS7 appearance, auto layout is still turned off for me.
And then i accidentally clicked "Alway Upgrade" so Xcode automatically upgrades all my xibs to Xcode 5 and iOS7 prior. But i use Xcode 4.x parallel and it's very annoying to switching back all the xibs when i accidentally open them in Xcode 5.
Before opened in XCode 5 interface builder:
After opened in XCode 5 interface builder:
I searched in Xcode and on Google to get the way to turn this "feature" off, but i still have no luck about it.