This is a bug in NSURL which managed to astonish me. Even as a seasoned developer you can only but marvel at the easy way to reproduce it and wonder what might be the reason for it happening.
A client reported that our app was crashing. When I launched the app in debugger I expected to see the exception to be something obvious, like a nil being unwrapped. But it turns out that there is a bug in NSLog. Filed as Radar rdar://24406969 and on Open Radar.