I have the following issue with a moving head, but I can reproduce it with a generic dimmer channel.
Steps:
- add a generic dimmer
- With the fader in the mixer (simple workspace) (moving from bottom to top) I changed the value from 0 to 255: Works. Checked it with the DMX channel monitor
- Edit channel properties and activate the modifier "Invert"
- Move the fader from bottom to top gives the values from 255 to 0: Works as expected
- Edit channel properties again and reset the modifiers
- Move the fader from bottom top: The output-field above the fader shows 0 in the most bottom position, the DMX channel monitor 255!!! Moving the fader slightly up, the output field above the fader shows1 and also the DMX channel monitor shows1. Moving the fader to the top, the output field and the DMX monitor shows the same values. Moving back to bottom, both values decreases to 1 and at the most bottom position the output field above the fader shows 0 and the DMX monitor shows 255 again.
With this behavior I can not use the moving head with inverted PAN channel

In my case, I can invert the PAN at the Hardware-Settings of the MH....
Is is in QLC+ 4.12.4 on Debian Buster.
Best regards from Germany

Holger