I know what you're thinking, "it's supposed to do that." But hear me out:
The filter does not affect the sound at all, and at a certian point it just cuts the signal completely. And I do not know why. I think it's because the "v" in the gain/vca is coming from a potentiometer, but I'm not sure. The filter is the demo 4 pole filter example.
here's a picture: http://imgur.com/mNAOvYG
so, when you disconnect the gpio and instead use a dial directly from the patcher it behaves differently?
The gpio/in/analog works the same like when you would connect a ctrl/dial p object to the pitch inlet of your filter. This means that these are only positive values. So you need to convert the incoming signal to a bipolar signal with a conv/unipolar2bipolar object. Best to leave the pitch dial of the filter object at 0.00 as well, so your potentiometer will controll the full range of the filter.
The resonance inlet of the filter can be connected directly to gpio/in/analog, since the resonance dial goes from 0 to 64.