According to the spec, sending security request should result in pairing if devices are not bonded, or setting up the encryption, if devices are already bonded. So if you are already bonded, your application should be waiting for encryption changed callback rather than SMP result callback. Application can check if it is paired with the device at the time when connection is established, by calling emconninfo_deviceBonded().
It actually works correctly in iOS 8 (and it used to work correctly in iOS 5). In 6 and 7 when phone received SMP request it would erroneously start pairing even if devices are already paired.
