Solo'ing a Return group makes the sounds stop playing.

Maybe this mixer is different and this is intentional, but in Ableton Live you are able to solo a return channel and listen back to the signal.

To reproduce:
- Open attached project and launch "AudioMixerTest" scene
- Open the window for audio mixer asset "Ambience" and duck it
- Make sure that one of the audio groups has a send/return or effect on it
- Hit Play and observe that there is green attenuation levels on the audio groups as well as the Send/Return channels
- Solo a return Return channel
- Observe that the audio groups stops playing