Reproduction steps:
1. Open the attached project "test Unity labs audio.zip";
2. Open the Audio Mixer Tab;
3. Enter a play mode;
4. Observe that there have to be 3 sounds playing - Harp, Male and Female voices;
5. Press Mute on the Harp sound (it is muted as expected);
6. Press Mute on the VO Group (Male and female voices should be muted, but they're not);
7. Press Mute on the Master sound (same as with VO Group).

Expected results: Male and Female voices sounds should be muted when pressing Mute on the VO Group and Master.
Actual results: Sounds are still playing in the scene.

Reproduced on: 5.5.0f3, 5.5.2p2, 5.6.0b10, 5.6.0f1, 2017.1.0a3.