As spotted by
XDA Developers, it looks like Android P will also block idle background apps from accessing the microphone. Needless to say, the possibility that an app could be recording users without their knowledge — as long as it had, at some point, been granted permission to access the microphone — is a gross violation of privacy. Of course, there are some situations where you might actually want an app to continue recording audio while in the background, so hopefully they'll be some way to allow for that in Android P.