I updated to Xcode 6.1 to fix an error I was having with the Interface Builder Cocoa Touch Tool spiking to 99% CPU usage when I used the storyboard, which would freeze Xcode
Another workaround is to add constraints to the layout Before resizing of any views. (add missing constraints e.g.). The bug only seems to occur when there are no constraints available. I have reported the bug to Apple with Bugreporter.
Edit: So, at least it seems that Apple Bugreporter is working. The problem is fixed in XCode v 6.1.1.