AVAudioSession.currentRoute.inputs.count

I am setting the `AVAudioSessionCategoryPlayback` and then running the Voice Processing IO AudioUnit. In my test, when I am checking the AVAudioSession's currentRoute.inputs.count, it is not returning the consistent result. Following is my observation -


Returns 0 for iPhone 7 plus running iOS 12 Beta

Returns 0 for iPhone 6s running iOS 11.0

Returns 1 for iPhone 6 running iOS 11.4.1

Returns 1 for iPad pro running iOS 11


I was expecting when the category is set to `AVAudioSessionCategoryPlayback`, AVAudioSession's currentRoute.inputs.count should always return 0. Is this an incorrect expectation?