The display is stuck on zoomed in. I did a clean install Xcode install and it's still broken.
I just updated to the Xcode 6.2 Beta and it works on the retina display of my macbook. Unfortunately it just shows a white screen on my main monitor ...
Maybe the want to force me to use the MB screen as a simulator display ;-)
Having the same issue since the Yosemite beta update.
It's definitely not a permanent fix but moving the simulator to a screen with a different pixel scale factor makes the simulator usable on one or another of the screens.
来源：https://stackoverflow.com/questions/27068162/ios-8-and-xcode-6-simulator-display-out-of-alignment