iOS openurl deep link crashes app and device

I've set up deep links to work with my app, calling back to the following function in the app delegate:

- (BOOL)application:(UIApplication *)application
            openURL:(NSURL *)url
  sourceApplication:(NSString *)sourceApplication
         annotation:(id)annotation;

If the app has previously been opened then you can open a link from Safari, such as:

myapp://foo/bar

It opens the app without issue and processes the link fine.

However if you kill the app (using the app switcher) and then open the same link from Safari, it will crash the app in the simulator or crash the device on an iPhone 5s running iOS 8.1.3.

But I don't understand why?

I've tried removing the application:sourceApplication:annotation: function from the app delegate, and it still crashes if the app is not running. (If it is running it opens the app fine).

Any ideas?