Filter knobs set to relative are not working properly - APC40

I mapped some knobs to adjust filter and because I did not want to have the knobs go to complete effect (resulting in silence) I mapped them with relative increments and set that to 60%. That way I cannot kill the track completely.

However, when I start Traktor, the range is often not -60 to 60 percent but -20 to 100. I then have to remap the knob before each session which is annoying. Any ideas what's the problem?