QSound overrides system volume settings and sets it to max (Windows)

Steps to repro:
1. Use QSound in your application and play some wav files.
2. Open Volume Mixer, find your application and decrease volume to e.g. half of scale.
3. Play sound again in your app.

Expected result:
Sound volume does not change.

Actual result:
Sound volume in system Volume Mixer for the application is back to max.

After some investigation it looks like this is caused by QWindowsAudioOutput::open() function where setVolume(volumeCache) is called. volumeCache is always set to 1.0 (max) and every time you play a play a sound it overrides existing volume with volumeCache.