[SoundPage] Volume decreases when leaving the page

[moWerk]

When setting volume to e.g. 90, then leaving the soundPage and reopening it, the Intselector shows 89, not 90.
Setting to 80 and restarting the page shows 88, dreasing by 2.
When 50, it goes to 47.
At 40 it decreases to 36. Settings 30 likewise decreasing by 4 to 26.
20 decreases to 15, down by 5. 10 likewise decreses by 5 to 5.

I can see in dconf dump that the preMuteLevel is set to the decreased value when toggling mute.

Since the values are stable during runtime of the page, i figure the problem could be in VolumeControl.cpp?

[beroset]

I can verify this. How to reproduce:

1. go to Sound page
2. note the value (it's 52 on my watch right now)
3. increase volume with +
4. note the value (it's now 62)
5. leave Sound and go back to Settings
6. re-enter Sound and note the value (57)

It has a very similar effect if we go the other way and decrease the volume (52 -> 42 -> 36).