This also happens with Genos. I believe the Filter normally works to achieve its effects by changing the Resonance at certain points in its operating range. Normally you may not notice this but I would say the knob assigned to resonance is being "honest" by highlighting what happens to resonance values when you change the filter. You still have the option to turn the resonance back to where you want it.
Instead of assigning to Filter you probably have the option to assign that knob to Cut Off, which should not interfere automatically with Resonance. Making cut off negative (with resonance zero) should eventually reduce the brightness of the voice say at around minus 20 to minus 40. Then if you simultaneously increase the resonance to plus 20 to 40 you will hear varying degrees of "filtered" voices. Eg. Depending on the sample, Trumpet becomes a more jazzy tone and, and eventually muted trumpet effects and so on (not all of which may be desirable sounds!).
John
