Dim Inactive (addhelper) plugin: "Opacity" fade too fast compared to "Brightness"

[MC Return]

[How to reproduce]

1. Open CCSM->Dim Inactive->Misc. Options Tab
2. Set "Opacity" to 50 "Saturation" to 100 (not working at the moment anyway, see bug #1170983)
3. Activate it (default:"Super+p")

[What you would expect to happen]

All windows except the active one should dim and smoothly fade to:
Brightness: 30%
Saturation: 100%
Opacity: 50%

[What actually happens]

All windows except the active one dim and fade to:
Brightness: 30%
Saturation: 100%
Opacity: 50%

but the opacity fade is much faster and finishes first, while the brightness
takes much more time to finish.