Aurasma does not release audio resources

I am writing an iphone application where I also use Aurasma sdk for augmented reality. The app for other things uses a microphone. At the beginning, the microphone works fine. If I call Aurasma and return, the audio resource will not be released from Aurasma (and the microphone is not working properly). Do you have an idea how to fix these problems? Of course, we already call [audioManager stopAudioRecording] before starting aurasma and [audioManager startAudioRecording] when returning from aurasma.