Lmms: Monstro's osc 3 vol knob always uses percentages.

[Sawuare]

Monstro's osc 3 vol knob with the "Display volume as dBFS" setting enabled:

It uses percentages instead of levels in dBFS.

[zonkmachine]

The other volume knobs has line to set them explicitly as a volume knob.
m_osc2VolKnob -> setVolumeKnob( true );
Try adding a line like that for m_osc3VolKnob, may be all that's missing in there.

[Sawuare]

Tested your suggestion, it fixes the issue and works as expected. Will open a PR soon.
Which branch should I target, stable-1.2 or master?

[zonkmachine]

Bug fix, stable-1.2 would be fine.