[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?