Livestream: audio comes always from presenter stream

How to reproduce:

• create a livestream course element with two streams
• OK: when showing this multi-stream, the audio comes from the presenter stream
• in the course editor --> configuration tab: change the setting to show only stream 2 (= content stream)
• NOK: when showing the stream, the audio still comes from stream 1 (= presenter)
• OK: if only one stream is shown, the audio should come from this stream