AudioSource example: changing source has no effect

I'm running the AudioSource example on an Android tablet (Galaxy S8) with a bluetooth headset connected.

After selecting said headset from the dropdown menu, the example still show audio levels from the integrated mic. 

I test this by gently tapping on the tablet's mic with a finger. This produces almost no audible sound, but it is enough to saturate the integrated mic level.

The following warning is displayed when selecting the device: W Audio_Source_Test: QIODevice::write (AudioInfo): device not open